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| United States Patent |
5,557,014
|
|
Grate
, et al.
|
September 17, 1996
|
Catalytic system for olefin oxidation to carbonyl products
Abstract
The present invention provides aqueous catalyst solutions useful for
oxidation of olefins to carbonyl products, comprising a palladium catalyst
and a polyoxoacid or polyoxoanion oxidant comprising vanadium. It also
provides processes for oxidation of olefins to carbonyl products,
comprising contacting olefin with the aqueous catalyst solutions of the
present invention. It also provides processes for oxidation of olefins to
carbonyl products by dioxygen, comprising contacting olefin with the
aqueous catalyst solutions of the present invention, and further
comprising contacting dioxygen with the aqueous catalyst solutions. In
certain aqueous catalyst solutions and related processes of the present
invention, the solution has a hydrogen ion concentration greater than 0.10
mole per liter when essentially all of the oxidant is in its oxidized
state. In other aqueous catalyst solution and related processes of the
present invention, the solution is essentially free of sulfuric acid and
sulfate ions.
| Inventors:
|
Grate; John H. (Mountain View, CA);
Hamm; David R. (Mountain View, CA);
Klingman; Kenneth A. (San Mateo, CA);
Saxton; Robert J. (West Chester, PA);
Downey; Shannan J. (Fremont, CA)
|
| Assignee:
|
Catalytica, Inc. (Mountain View, CA)
|
| Appl. No.:
|
558202 |
| Filed:
|
November 16, 1995 |
| Current U.S. Class: |
568/401; 568/360; 568/478 |
| Intern'l Class: |
C07C 045/35 |
| Field of Search: |
568/360,401,478
|
References Cited
U.S. Patent Documents
| 3119875 | Jan., 1964 | Steinmetz | 260/604.
|
| 3122586 | Feb., 1964 | Berndt | 260/586.
|
| 3154586 | Oct., 1964 | Bander | 260/596.
|
| 3485877 | Dec., 1969 | Hargis | 260/604.
|
| 4146574 | Mar., 1979 | Onada | 423/299.
|
| 4404397 | Sep., 1983 | Daniel | 562/546.
|
| 4434082 | Feb., 1984 | Murtha | 502/164.
|
| 4448892 | May., 1984 | Kukes | 502/164.
|
| 4507506 | Mar., 1985 | Shioyama | 568/401.
|
| 4507507 | Mar., 1985 | Murtha | 568/401.
|
| 4532362 | Jul., 1985 | Kukes | 568/401.
|
| 4550212 | Oct., 1985 | Shioyama | 568/401.
|
| 4720474 | Jan., 1988 | Vasilevskis | 502/165.
|
| 4723041 | Feb., 1988 | Vasilevskis | 568/401.
|
| 4762817 | Aug., 1988 | Logsdon | 502/329.
|
| 5004845 | Apr., 1991 | Bradley | 568/885.
|
| Foreign Patent Documents |
| 828603 | Oct., 1975 | BE.
| |
| 0031729 | Jul., 1981 | EP.
| |
| 123085 | Nov., 1976 | DE.
| |
| 61-43131 | Mar., 1986 | JP.
| |
| 1508331 | Apr., 1978 | GB.
| |
Other References
Smidt, J., et al., "The Oxidation of Olefins with Palladium Chloride
Catalysts", Angew. Chem. Internat. Edit. vol. 1, pp. 80-88.
Miller, S. A., editor, Ethylene and Its Industrial Derivatives (published
by Ernest Benn Ltd, London, 1969), Chapter 8, pp. 639-689.
Matveev, K. I., et al., Kinetika i Kataliz (1977) vol. 18, No. 2, pp.
380-386. The English translation edition, "Kinetics of Oxidation of
Ethylene to Acetaldehyde by Phosphomolybdicvanadic Heteropolyacids in the
Presence of a Pd(II) Aquo Complex", pp. 320-326, is provided.
Polotebnova, N. A., et al., Zh. Neorg. Khim. (1973) 18:413. The English
translation edition, "Properties of Vanadomolybdophosphoric Acids with
Varying Concentrations of Molybdenum and Vanadium", Russian Journal of
Inorganic Chemistry (1973) 18(2):216-219, is provided.
Zangen, M., "Solvent Extraction From Molten Salts. V. Zinc(II) Chloride,
Bromide, and Iodide", Inorg. Chem., (1968) 7(1):133-138. Page 137 is
provided.
Matveev, K. I., Kinetika i Katal. (1977) vol. 18, No. 4, pp. 862-877. The
English translation edition, "Development of New Homogeneous Catalysts for
the Oxidation of Ethylene to Acetaldehyde", pp. 716-727, is provided.
Cihova, M., et al., "Catalytic Oxidation of Octene-1 in the Presence of
Palladium(II) Salts and Heteropolyacids", Reaction Kinetics and Catalysis
Letters, (1981) 16:383-386.
Cihova, M., et al., "Oxid acia 1-okt enu na 2-octan on v prieto cnom
reaktore", Ropa Uhlie (1986) 28:297-302. An English language abstract
(Chem. Abstr. 107(1):6740r) is attached.
El Ali, Bassam, et al., "Oxydation catalytique de l'oct ene-1 en pr esence
de complexes de rhodium(III) ou de palladium(II) associ es a des acides
phosphomolybdovanadiques et au dioxyg ene", J. Organomet. Chem. (1987)
327:C9-C14. The publication includes an English language abstract.
Kuznetsova, L. I., et al., "Catalytic Oxidation of Vanadyl Salts by Oxygen
in the Presence of Sodium Molybdate", Reaction Kinetics and Catalysis
Letters (1975) 3(3):305-310.
Kuznetsova, L. I., et al., Koordinatsionnaya Khimiya (1977) vol. 3., No. 1,
pp. 51-58. The English translation edition, "State of
Phosphomolybdovanadium Heteropoly Blue Oxides in Aqueous Solution", pp.
39-44, is provided.
Berdnikov, V. M., et al., Koordinatsionnaya Khimiya (1979) vol. 5, No. 1,
pp. 78-85. The English translation edition "Kinetics and Mechanism of the
Oxidation of Reduced Molybdovanadophosphoric Heteropolyacids with Oxygen
Hexavanadic Heteropoly Blues", pp. 60-66, is provided.
Kozhevnikov, I. V., Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya
(1981) No. 11., pp. 2428-2435. The English translation edition, "Mechanism
of the Oxidation of 12-Molybovanadophosphate Blue by Oxygen in Aqeuous
Solution", pp. 2001-2007, is provided.
Burov, Y. V., et al., Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya
(1980) No. 7, pp. 1469-73. The English translation edition, "Steady-Flow
Investigation of the Kinetics of the Reaction Between VO.sup.2+ and
Phosphorus-Molybdenum-Vanadium Heteropoly Anions", pp. 1017-1021, is
provided.
Kuznetsova, L. I., et al., "Mechanism of Oxidation of
Molybdovanadophosphoric Heteropoly Blues by Molecular Oxygen. Trivanadium
Heteropoly Blue", Reaction Kinetics and Catalysis Letters (1981)
17:401-406.
Davison, S. F., et al., "Phosphomolybdic Acid as a Reoxidant in the
Palladium(II)-catalysed Oxidation of But-1-ene to Butan-2-one", J. Chem.
Soc. Dalton Trans. (1984) pp. 1223-1228.
Davison, S. F., Ph.D. Dissertation, "Palladium and Heteropolyacid Catalyzed
Oxidation of Butene to Butanone", University of Sheffield, 1981. The
Summary, Table of Contents, pages 63 and 77, are provided.
Pope, Michael Thor, Inorganic Chemistry Concepts 8: Heteropoly and Isopoly
Oxometalates, published by Springer-Verlag, NY. A copy of the Table of
Contents is provided.
Koscielski, T., et al., "Catalytic Hydrogenation on Raney Nickel Catalyst
Modified by Chromium Hydroxide Deposition", Applied Catalysis (1989)
49:91-99.
Sixth World Petroleum Congress Proceedings, Section IV, Paper 40, pp.
461-466, Frankfurt, 19-26 Jun. 1963.
"New Process for Acetone and MEK: A Special Report: 6th World Petroleum
Congress", in Hydrocarbon Processing & Petroleum Refiner (1963) vol. 42,
pp. 149-152.
"Wacker Process Can Make Acetone, MEK", in Chemical and Engineering News, 8
Jul. 1963, pp. 50-51.
Bonnier, J-M., et al., "Raney Nickel as a Selective Catalyst for Aldehyde
Reduction in the Presense of Ketones", Applied Catalysis (1987) 30:181-184
.
|
Primary Examiner: Reamer; James H.
Attorney, Agent or Firm: Grate; John H.
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a for a continuation of prior patent application Ser.
No. 08/461,223, now abandoned, filed Jun. 5, 1995 entitled CATALYTIC
SYSTEM FOR OLEFIN OXIDATION TO CARBONYL PRODUCTS, which is a for a
continuation of prior patent application Ser. No. 07/689,050, now
abandoned, filed Sep. 4, 1992 entitled CATALYTIC SYSTEM FOR OLEFIN
OXIDATION TO CARBONYL PRODUCTS, which is a continuation-in-part of U.S.
patent application Ser. No. 489,806 filed Mar. 5, 1990, now abandoned,
which is incorporated by reference entirely. Related U.S. patent
applications Ser. Nos. 07/689,048 filed Sep. 4, 1992, now abandoned, and
07/675,932, filed Sep. 2, 1992 now abandoned, 07/934,643 filed Sep. 4,
1992 co-filed with Ser. No. 07/689,050, now abandoned, are each
incorporated by reference entirely.
Claims
We claim as our invention:
1. In an aqueous catalyst solution for the oxidation of an olefin to a
carbonyl product comprising a palladium catalyst, a polyoxoanion oxidant
comprising vanadium, and hydrogen ions, the improvement comprising
providing a concentration of said hydrogen ions greater than 0.10 mole per
liter of solution when essentially all the oxidant is in its oxidized
state, and providing said solution essentially free of sulfuric acid and
sulfate ions.
2. The solution of claim 1 wherein said polyoxoanion oxidant further
comprises phosphorus and molybdenum.
3. The solution of claim 2 wherein said polyoxoanion oxidant comprises a
phosphomolybdovanadate having the formula
[H.sub.y PMo.sub.(12-x) V.sub.x O.sub.40 ].sup.(3+x-y)-
wherein 0<x<12 and 0.ltoreq.y<(3+x), or mixtures thereof.
4. The solution of claim 1 further comprising at least one of an olefin and
a corresponding carbonyl product.
5. In a Wacker process for the manufacture of acetaldehyde by oxidation of
ethylene using an aqueous catalyst solution, the improvement wherein the
aqueous catalyst solution is the solution of claim 1.
6. A process for oxidation of an olefin to a carbonyl product comprising:
contacting the olefin with an aqueous catalyst solution, wherein the
aqueous catalyst solution is the solution of claim 1.
7. In a process for oxidation of an olefin to a carbonyl product comprising
reacting the olefin with an aqueous catalyst solution comprising a
palladium catalyst, a polyoxoanion oxidant comprising vanadium, and
hydrogen ions, the improvement comprising providing a concentration of
said hydrogen ions greater than 0.10 mole per liter of solution when
essentially all the oxidant is in its oxidized state, and providing said
aqueous catalyst solution essentially free of sulfuric acid and sulfate
ions.
8. The process of claim 7 wherein said polyoxoanion oxidant further
comprises phosphorus and molybdenum.
9. The process of claim 8 wherein said polyoxoanion oxidant comprises a
phosphomolybdovanadate having the formula
[H.sub.y PMo.sub.(12-x) V.sub.x O.sub.40 ].sup.(3+x-y)-
wherein 0<x<12 and 0.ltoreq.y<(3+x), or mixtures thereof.
10. The process of claim 7 wherein the olefin is ethylene and the carbonyl
product is acetaldehyde.
11. The process of claim 7 wherein the olefin is propylene and the carbonyl
product is acetone.
12. The process of claim 7 wherein the olefin is one of 1-butene,
cis-2-butene, and trans-2-butene, or mixtures thereof, and the carbonyl
product is 2-butanone.
13. The process of claim 7 wherein the olefin is one of 3-methyl-1-butene
and 2-methyl-2-butene, or mixtures thereof, and the carbonyl product is
3-methyl-2-butanone.
14. The process of claim 7 wherein the olefin is 4-methyl-1-pentene and the
carbonyl product is 4-methyl-2-pentanone.
15. The process of claim 7 wherein the olefin is cyclopentene and the
carbonyl product is cyclopentanone.
16. The process of claim 7 wherein the olefin is cyclohexene and the
carbonyl product is cyclohexanone.
17. The process of claim 7 further comprising contacting dioxygen with the
aqueous catalyst solution.
18. The process of claim 7 further comprising the steps of removing the
carbonyl product from the aqueous solution, contacting dioxygen with the
aqueous catalyst solution at conditions sufficient to regenerate the
oxidant in its oxidized state, and contacting additional olefin with the
aqueous catalyst solution.
19. In an aqueous catalyst solution for the oxidation of an olefin to a
carbonyl product comprising a palladium catalyst, a polyoxoanion oxidant
comprising vanadium, and hydrogen ions, the improvement comprising
providing said solution essentially free of sulfuric acid and sulfate ions
.
Description
FIELD OF THE INVENTION
This invention relates generally to oxidation of olefins to carbonyl
compounds. More specifically, it relates to oxidation of olefins to
carbonyl compounds by polyoxoanion oxidants in aqueous solution, catalyzed
by palladium. In another aspect, it relates to reoxidation of reduced
polyoxoanions in aqueous solution by reaction with dioxygen. It further
relates to an overall process for the oxidation of olefins to carbonyl
compounds by dioxygen catalyzed by palladium and polyoxoanions in aqueous
solution.
BACKGROUND OF THE INVENTION
The catalyst solutions and the processes of the present invention are
useful for the production of aldehydes, ketones, and carboxylic acids,
which are chemicals of commerce and/or feedstocks for the production of
chemicals and materials of commerce. For example, acetone, methyl ethyl
ketone and methyl isobutyl ketone are used as solvents. Acetaldehyde is
used in the production of acetic acid, polyols, and pyridines. Acetic acid
is used in the production of vinyl acetate, cellulose acetate, and various
alkyl acetate esters which are used as solvents. Acetone is used in the
production of methylmethacrylate for polymethylmethacrylate. Cyclohexanone
is used in the production of caprolactam for nylon-6 and adipic acid for
nylon-6,6. Other cyclic ketones can be used for the production of other
nylon-type polymers.
Acetaldehyde is industrially produced by the Wacker oxidation of ethylene
by dioxygen, which uses an aqueous catalyst system of palladium chloride,
copper chloride, and hydrochloric acid to accomplish the following net
conversion:
C.sub.2 H.sub.4 + 1/2O.sub.2 .fwdarw.CH.sub.3 CHO (1)
Reviews of the Wacker process chemistry and manufacturing processes for the
direct oxidation of ethylene to acetaldehyde can be found in "The
Oxidation of Olefins with Palladium Chloride Catalysts", Angew. Chem.
internat. Edit., Vol. 1 (1962), pp. 80-88, and in Chapter 8 of Ethylene
and its Industrial Derivatives, S. A. Miller ed., Ernest Benn Ltd.,
London, 1969, each of which is incorporated by reference entirely. Aspects
of Wacker technology are also disclosed in U.S. Pat. Nos. 3,122,586,
3,119,875, and 3,154,586, each incorporated by reference entirely.
In the Wacker process chemistry, ethylene is oxidized by cupric chloride in
aqueous solution, catalyzed by palladium:
##STR1##
In a typical manufacturing operation, copper is present in the aqueous
solution at concentrations of about 1 mole per liter, total chloride is
present at concentrations of about 2 moles per liter, and the palladium
catalyst is present at concentrations of about 0.01 moles per liter. Under
these conditions, palladium(II) exists predominantly as the
tetrachloropalladate ion, PdCl.sub.4.sup.=. Cuprous chloride resulting
from the oxidation of ethylene is solubilized in the aqueous solution by
the co-produced hydrochloric acid, as the dichlorocuprate ion, Cu.sup.I
Cl.sub.2.sup.-. In a subsequent Wacker chemistry step, this reduced copper
is reoxidized by reaction with dioxygen:
2 Cu.sup.I Cl.sub.2.sup.- +2 H.sup.+ +1/2O.sub.2 .fwdarw.2 Cu.sup.II
Cl.sub.2 +H.sub.2 O (3)
(Reactions (2) and (3) combined give overall reaction (1)).
Two acetaldehyde manufacturing processes, a two-stage process and a
one-stage process, have been developed and operated using the Wacker
system chemistry. In the two-stage process, ethylene oxidation by cupric
chloride, reaction (2), and reoxidation of cuprous chloride by air,
reaction (3), are conducted separately, with intermediate removal of the
acetaldehyde product from the aqueous solution. The reoxidized aqueous
solution is recycled to the ethylene oxidation stage. The reactions are
conducted at temperatures of about 100.degree. to 130.degree. C. in
reactors which, by providing very efficient gas-liquid mixing, result in
high rates of diffusion (mass transfer) of the reacting gas into the
aqueous solution. Under these conditions, about 0.24 moles ethylene per
liter of solution can be reacted within about 1 minute in the ethylene
reactor, corresponding to an average ethylene reaction rate of about 4
(millimoles/liter)/second. With a typical palladium concentration of about
0.01 moles per liter, this corresponds to a palladium turnover frequency
(a measure of catalyst activity) of about 0.4 (moles C.sub.2 H.sub.4 /mole
Pd)/second. In the air reactor, about 0.12 moles dioxygen per liter of
solution can be reacted within about 1 minute, corresponding to an average
dioxygen reaction rate of about 2 (millimoles/liter)/second.
In the one-stage process, ethylene and dioxygen are simultaneously reacted
with the aqueous solution, from which acetaldehyde is continuously
removed.
Palladium catalyzes the oxidation of ethylene by cupric chloride (reaction
(2)) by oxidizing ethylene (reaction (4)) and then reducing cupric
chloride (reaction (5)):
C.sub.2 H.sub.4 +PdCl.sub.4 =+H.sub.2 O.fwdarw.CH.sub.3 CHO+Pd.sup.0 +2
H.sup.+ +4 Cl.sup.- ( 4)
Pd.sup.0 +4 Cl.sup.- +2 Cu.sup.II Cl.sub.2 .fwdarw.PdCl.sub.4.sup.= +2
Cu.sup.I Cl.sub.2.sup.= ( 5)
Functionally, the copper chlorides mediate the indirect reoxidation of the
reduced palladium(0) by dioxygen via reaction (5) plus reaction (3).
Direct oxidation of palladium(0) by dioxygen is thermodynamically possible
but is far too slow for practical application.
The overall rate of oxidation of ethylene by the Wacker system is limited
by the rate of oxidation of ethylene by the tetrachloropalladate (reaction
(4)). The reaction rate is inversely dependent on both the hydrogen ion
concentration and the square of the chloride ion concentration, having the
following concentration dependencies:
C.sub.2 H.sub.4 reaction rate.varies.[PdCl.sub.4.sup.= ][C.sub.2 H.sub.4
]/[H.sup.+ ][Cl.sup.- ].sup.2 ( 6)
Two chloride ions must be dissociated from tetrachloropalladate before
palladium(II) productively binds both the substrates of reaction (4),
ethylene and water. Said another way, chloride competes with the two
substrates for the third and fourth coordination sites on palladium(II).
This occurs by the following equilibria:
PdCl.sub.4.sup.= +C.sub.2 H.sub.4 .revreaction.PdCl.sub.3 (C.sub.2
H.sub.4).sup.- +Cl.sup.- ( 7)
PdCl.sub.3 (C.sub.2 H.sub.4).sup.- +H.sub.2 O.revreaction.PdCl.sub.2
(C.sub.2 H.sub.4)(H.sub.2 O)+Cl.sup.- ( 8)
Not only does chloride ion competitively inhibit the binding of substrates,
but the remaining bound chlorides in intermediate complexes diminish the
electrophilicity (positive charge density) at the palladium(II) center
which drives the overall reaction to palladium(0). The subsequent reaction
steps, hydrogen ion dissociation (reaction (9)) and collapse of the
resulting intermediate to products (reaction (10)), are less favored for
these chloride-bound intermediate complexes that they would be for their
aquated counterparts with fewer or no bound chlorides.
PdCl.sub.2 (C.sub.2 H.sub.4)(H.sub.2 O).revreaction.PdCl.sub.2 (C.sub.2
H.sub.4)(OH).sup.- +H.sup.+ ( 9)
PdCl.sub.2 (C.sub.2 H.sub.4)(OH).sup.- .fwdarw..fwdarw..fwdarw.CH.sub.3
CHO+Pd.sup.0 +H.sup.+ +2 Cl.sup.- ( 10)
A step in reaction (10) is turnover rate-limiting for reaction (4)in the
Wacker system (reactions (7), (8), (9), and (10) give reaction (4)), so
that the disfavoring influences of chloride ion on reaction (10) and on
the preceding equilibria (7), (8), and (9) are manifested in the obtained
palladium catalyst activity.
However, the Wacker system requires a high total chloride concentration to
function effectively. The chloride to copper ratio must be greater than
1:1 for the copper(II) to be soluble CuCl.sub.2 rather than insufficiently
soluble copper hydroxide chlorides, and for copper(I) to be soluble
CuCl.sub.2.sup.- rather than insoluble CuCl. Moreover, in the absence of
chloride, aquated copper(II) is thermodynamically impotent for oxidizing
palladium(0) metal to aquated palladium(II). Chloride complexation raises
the copper(II)/copper(I) oxidation potential and lowers the
palladium(II)/palladium(0) oxidation potential, so that at high chloride
ion concentrations the forward reaction (5) becomes thermodynamically
favored.
The Wacker system has several undesirable characteristics in the
manufacture of acetaldehyde. These undesirable characteristics result from
the high cupric chloride concentration. The aqueous cupric chloride
solution is extremely corrosive; manufacturing process equipment is
constructed of expensive corrosion resistant materials, usually titanium.
The manufacturing processes typically convert a percent or more of the
ethylene feed to chlorinated organic by-products. These chlorinated
organic by-products are hygienically and environmentally objectionable.
Their adequate separation from the acetaldehyde product and from other gas
and liquid streams which exit the process and their proper destruction or
disposal add to the operating costs of the manufacturing processes.
These chlorinated organic by-products have a number of mechanistic origins.
Some result from direct additions of hydrochloric acid to ethylene, giving
ethylchloride, and to olefinic by-products. Others result from palladium
centered oxychlorination, for example, 2-chloroethanol from ethylene. The
predominant origin of chlorinated organic by-products is oxychlorination
by cupric chloride; most arise from copper centered oxychlorination of
acetaldehyde, giving chloroacetaldehydes, and further reactions of the
chloroacetaldehydes. Accordingly, we determined that most of the
objectionable chlorinated organic by-product yield results not simply from
the presence of chloride, but from the combination of chloride and copper.
Aqueous palladium(II) salts also oxidize higher olefins to carbonyl
compounds according to equation (11), where R, R', and R" are hydrocarbyl
substituent groups and/or hydrogen (R.dbd.R'.dbd.R".dbd.H for ethylene):
##STR2##
As examples, aqueous palladium(II) salts oxidize propylene to acetone (and
some propionaldehyde), butenes to methyl ethyl ketone (and some
butyraldehyde), and cyclohexene to cyclohexanone. Higher olefins can be
oxidized by dioxygen using the Wacker system, but serious problems
encountered in using the Wacker system to oxidize higher olefins have
effectively prohibited any other significant application to manufacturing
carbonyl compounds.
The rate of oxidation of the olefinic double bond by aqueous palladium(II)
salts generally decreases as the number and/or size of hydrocarbyl
substituents increases. This decrease in rate is particularly severe with
PdCl.sub.4.sup.= in the Wacker system, due to the competition of chloride
with the more weakly binding higher olefins for palladium(II) complexation
and due to the lowered electrophilicity of multiply chloride-bound
olefin-palladium(II)intermediates. Consequently, much higher palladium
concentrations (with its concomitant palladium investment) are necessary
to obtain volumetric production rates of higher carbonyl compounds
comparable to acetaldehyde production rates.
An even more prohibitive disadvantage of the Wacker system for
manufacturing carbonyl compounds from higher olefins is the substantially
increased production of chlorinated organic by-products. Higher olefins
are more susceptible to palladium centered oxychlorination, which
chlorinates not only at olefinic carbon atoms but also at allylic carbon
atoms. Higher aldehydes and ketones having methylene groups adjacent to
the carbonyl group are also more susceptible to cupric chloride mediated
oxychlorination than is acetaldehyde. As a result, the productivity of the
Wacker system for producing chlorinated organic by-products increases
rapidly both with increasing number and size of hydrocarbyl substituents
in the olefin.
Other, multistep manufacturing processes are typically used instead of the
Wacker process to convert higher olefins into corresponding carbonyl
compounds. For example, the manufacture of methyl ethyl ketone
(2-butanone) involves the reaction of n-butenes with concentrated sulfuric
acid to produce sec-butyl hydrogen sulfate and hydrolysis of sec-butyl
hydrogen sulfate to obtain 2-butanol and diluted sulfuric acid. 2-butanol
is catalytically dehydrogenated to produce methyl ethyl ketone. The
diluted sulfuric acid must be reconcentrated for recycle.
Other carbonyl compounds are instead manufactured from starting materials
more expensive than the corresponding higher olefin. For example,
cyclopentanone is manufactured from adipic acid instead of from
cyclopentene.
An effective method for the direct oxidation of higher olefins to carbonyl
compounds by dioxygen has been long sought in order to enable more
economical manufacturing of carbonyl compounds. Yet, in 30 years since the
development of the Wacker system, no alternate palladium-based system for
the oxidation of olefins by dioxygen which avoids the disadvantages and
limitations of the Wacker system has been successfully applied in
commercial manufacturing operation.
Systems have been proposed which use polyoxoanions, instead of cupric
chloride, in combination with palladium to effect the oxidation of
olefins.
U.S. Pat. No. 3,485,877, assigned to Eastman Kodak Company (hereafter,
"Eastman patent") discloses a system for converting olefins to carbonyl
compounds by contacting with an agent comprising two components, one of
which is palladium or platinum, and the other is molybdenum trioxide or a
heteropolyacid or salt thereof. This patent discloses that the so-called
"contact agent" may be in an aqueous solution for a liquid phase process,
but that it is advantageous and preferred to support the agent on a solid
carder for a vapor phase process in which gaseous olefin is contacted with
the solid phase agent. The patent compares the oxidation of propylene with
a liquid phase contact agent (in Example 16), to give acetone
substantially free of by-products with the oxidation of propylene in the
vapor phase with a corresponding solid contact agent (in Example 10), to
give acrolein. Apparently, the behavior of an olefin's liquid phase
reaction with the disclosed aqueous contact agent solution cannot be
predicted from the behavior of the olefin's vapor phase reaction with the
analogous solid contact agent.
Eastman patent discloses that, when operating in the liquid phase,
heteropolyacids or their salts, and particularly phosphomolybdic acid or
silicomolybdic acid in water are preferred. Among the heteropolyacids
disclosed, only phosphomolybdic acid and silicomolybdic acid are
demonstrated by working example. No salts of heteropolyacids are so
demonstrated. Phosphomolybdovanadic acid or salts thereof are nowhere
mentioned in this patent.
Eastman patent also discloses the reaction in the presence of oxygen or
oxygen containing gas. It also discloses periodic regeneration of the
contact agent with air. However, the use of oxygen or air is demonstrated
by working examples only for reactions of olefins in the vapor phase with
solid phase contact agents.
We have found that oxygen reacts too slowly with reduced phosphomolybdic
acid or silicomolybdic acid in aqueous solutions for such solutions to be
practically useful in the industrial conversion of olefins to carbonyl
compounds using oxygen or air as oxidant. In contrast, our reduced
polyoxoanions comprising vanadium in aqueous solution of the present
invention can react rapidly with oxygen or air.
In addition, Eastman patent discloses palladium chlorides among various
preferred palladium or platinum components for the contact agent.
Palladous chloride is predominantly used among the working examples.
Eastman patent also discloses that it is possible to improve the action of
the contact agent by incorporating small amounts of hydrochloric acid or
ferric chloride. However, the only demonstration by working example adds
ferric chloride in a solid phase contact agent for a vapor phase reaction
(Example 19) to obtain higher reaction rates (conversion and space time
yield). No such demonstration, nor result, is given for addition of
hydrochloric acid to either a solid or a liquid phase contact agent, nor
for addition of either hydrochloric acid or ferric chloride to a liquid
phase contact agent.
Belgian Patent No. 828,603 and corresponding United Kingdom Patent No.
1,508,331 (hereafter "Matveev patents") disclose a system for the liquid
phase oxidation of olefins employing an aqueous solution combining: a) a
palladium compound; b) a reversible oxidant which has a redox potential in
excess of 0.5 volt and which is a mixed isopolyacid or heteropolyacid
containing both molybdenum and vanadium, or a salt of said polyacid; and,
c) an organic or mineral acid other than said mixed isopolyacid or
heteropolyacid, which organic or mineral acid is free of halide ions and
is unreactive (or at most weakly reactive) with the palladium compound.
The disclosed system differs from that of Eastman patent by simultaneously
employing only certain heteropolyacids and mixed isopolyacids and adding
certain other acids to the solution. Those certain polyacids employed
contain both molybdenum and vanadium. Those certain other acids added are
not the polyacid and are free of halide ions.
Matveev patents disclose that only the certain polyacids, containing both
molybdenum and vanadium, function satisfactorily in the system as
reversibly acting oxidants, wherein the reduced form of the oxidant is
reacted with dioxygen to regenerate the oxidant. The patent further
discloses that the polyacid used contains from 1 to 8 vanadium atoms, more
preferably 6 atoms, in a molecule with molybdenum. According to the
disclosure, as the number of vanadium atoms increases from 1 to 6 the
principal characteristics of the catalyst, such as its activity,
stability, and olefin capacity, increase.
Matveev patents disclose typical heteropolyacids of a formula H.sub.n
[PMo.sub.p V.sub.q O.sub.40 ], in which n=3+q, p=12-q, q=1 to 10. Matveev
patents disclose that the catalyst is prepared, in part, by dissolving in
water, oxides, salts, and/or acids of the elements forming the polyacid
and then adding to the solution, the specified other organic or mineral
acid. A preferred catalyst is said to be prepared by dissolving in water
Na.sub.3 PO.sub.4 (or Na.sub.2 HPO.sub.4, or NaH.sub.2 PO.sub.4, or
H.sub.3 PO.sub.4, or P.sub.2 O.sub.5), MoO.sub.3 (or Na.sub.2 MoO.sub.4,
or H.sub.2 MoO.sub.4), V.sub.2 O.sub.5 (or NaVO.sub.3), and Na.sub.2
CO.sub.3 (or NaOH) to form a solution, adding PdCl.sub.2 to the solution
of molybdovanadophosphoric acid, and then adding the other acid. (Sulfuric
acid is the only such acid demonstrated by working example.) It is said to
be best if the total number of Na atoms per atom of P is not less than 6.
Heteropolyacids in the series designated H.sub.4 [PMo.sub.11 VO.sub.40 ]
to H.sub.11[PMo.sub.4 V.sub.8 O.sub.40 ] are said to be obtained, and are
said to be used in most of the working examples. (We have found that such
solutions prepared according to the methods disclosed in Matveev patents
are not actually solutions of free heteropolyacids, as designated by
formulas of the type H.sub.n [PMo.sub.p V.sub.q O.sub.40 ]. Instead, they
are solutions of sodium salts of partially or completely neutralized
heteropolyacids; that is, solutions of sodium polyoxoanion salts.)
According to Matveev patents, the activity and stability of the catalyst is
increased by the presence of certain other mineral or organic acids which
do not react (or react only feebly) with palladium and contain no halide
ions(e.g. H.sub.2 SO.sub.4, HNO.sub.3, H.sub.3 PO.sub.4, or CH.sub.3
COOH). The most preferable of the above acids is sulfuric acid, which is
said to increase the activity and stability of the catalyst whilst not
seriously increasing the corrosivity of the solution. Sulfuric acid is the
only acid which appears in the working examples. Matveev patents prescribe
that the amount of acid is enough to maintain the "pH" of the solution at
"not more than 3, preferably at 1.0". The working examples predominantly
recite "pH" 1. Matveev patents indicate that with "higher pH values", the
catalyst is not sufficiently stable with respect to hydrolysis and
palladium precipitation, and is of low activity in the olefinic reaction.
They further indicate that with "lower pH values", the rate of the oxygen
reaction is appreciably diminished. However, Matveev patents do not
disclose any method for determining the "pH" of the disclosed solutions,
nor do they specify anywhere how much sulfuric acid was added to achieve
the stated "pH" value.
The disclosure of Matveev patents is generally directed towards providing a
catalyst system having a reversibly acting oxidant (wherein the reduced
form of the oxidant can be reacted with dioxygen to regenerate the
oxidant) and having an absence of chloride ions. Mineral acids which
contain halide ions are specifically excluded from the certain other acids
added in the disclosed system. PdCl.sub.2 is among the palladium compounds
used in the working examples; it is the only source of added chloride
disclosed and is added only coincidental to the selection of PdCl.sub.2 as
the palladium source. PdCl.sub.2 and PdSO.sub.4 are generally disclosed to
be equivalent palladium sources.
Matveev patents' preferred palladium concentration in the catalyst is said
to be 0.002 g-atom/liter (2 mill/molar). This is the concentration
demonstrated in most of the working examples. In Example 9 of both Belgian
and British patents, a catalyst containing a very high concentration of
heteropolyacid, 1.0 g-mole/liter, and a very high concentration of
PdCl.sub.2, 0.5 g-atom/liter, is disclosed. This would mean that 1.0
g-atom/liter chloride is added as part of the palladium source. The stated
conclusion from this example is that the high viscosity and specific
gravity of such concentrated solutions adversely affect the mass transfer
conditions and make the process diffusion controlled and impractical. The
result reported for this test with 0.5 g-atom/liter PdCl.sub.2 is so poor,
especially in terms of palladium activity (see Table 1), as to lead one
away from attempting to use the example.
The results of selected working examples reported in Matveev patents are
presented in Table 1. The examples selected are those said to use a
phosphomolybdovanadic heteropolyacid in the oxidation of ethylene for
which quantitative results are reported. Data and results to the left of
the vertical bar in Table 1 are taken directly from the patent. Results to
the right of the vertical bar are calculated from the reported results.
The Example numbers are those used in Belgian 828,603.
Most working examples in Matveev patents report tests conducted in a
shaking glass reactor. Typical reaction conditions in this reactor were
90.degree. C. with 4.4 psi of ethylene, and separately with 4.4 psi of
oxygen. Among the examples collected in Table 1, those using the shaking
glass reactor with the preferred concentrations of heteropolyacid and
palladium (Examples 1-6) gave ethylene and oxygen rates of 0.089-0.156 and
0.037-0.086 (millimoles/liter)/second, respectively (see Table 1). Example
9, with 0.5 g-atom/liter PdCl.sub.2, is said to be diffusion controlled;
ethylene and oxygen reaction rates were 0.223 and 0.156
(mill/moles/liter)/second, respectively.
We have found that shaking reactors are generally poor devices for mixing
such gaseous reactants and liquid aqueous phases and the rate diffusion
(mass transfer) of gaseous reactants into an aqueous catalyst solution for
reaction is prohibitively slow in such reactors. Additionally, 4.4 psi of
ethylene is relatively too low a pressure for rapid dissolution of
ethylene into a aqueous catalyst solution.
TABLE 1
__________________________________________________________________________
Examples from Belgian Patent 828,603
__________________________________________________________________________
Reported:
C.sub.2 H.sub.4
C.sub.2 H.sub.4
O.sub.2
Ex..sup.1
[Pd].sup.3
Pd [HPA].sup.4
HPA
% xs
temp
P.sub.C.sbsb.2.sub.H.sbsb.4
rate
capacity
P.sub.O.sbsb.2
rate
No.
Rctr.sup.2
mM source
Molar
Vq.sup.5
V.sup.6
.degree.C.
mmHg
W.sup.9
mole/l
mmHg
W.sup.10
__________________________________________________________________________
1 sg 2 PdCl.sub.2
0.3 6 25 90 230 143
0.6 230 115
2 sg 2 PdCl.sub.2
0.3 8 35 90 230 248
0.8 230
3 sg 2 PdSO.sub.4
0.3 4 15 90 230 128
0.36 230 105
4 sg 2 PdCl.sub.2
0.3 3 10 90 230 120
0.25 230 70
5 sg 2 PdSO.sub.4
0.3 2 5 90 230 210
0.15 230 50
6 sg 2 PdCl.sub.2
0.2 6 25 90 230 190
0.3 230 60
6 ss 2 PdCl.sub.2
0.2 6 25 110
6 atm
900
0.3 3.5 atm
450
9 sg 500
PdCl.sub.2
1.0 6 25 90 230 300
3.0 230 210
10 sg 1 Pd metal
0.2 6 25 90 230 150
0.2 230 100
12 sg 1 PdSO.sub.4
0.1 5 ? 50 230 25
0.15 230 10
__________________________________________________________________________
Calculated:
C.sub.2 H.sub.4
Pd O.sub.2
Ex..sup.1
P.sub.C.sbsb.2.sub.H.sbsb.4
rate t.f.
Pd % V P.sub.O.sbsb.2
rate
No.
psi mM/s.sup.11
1/s.sup.12
TON.sup.7
red.sup.8
psi
mM/s.sup.13
__________________________________________________________________________
1 4.4 0.106
0.053
300 53 4.4
0.086
2 4.4 0.185
0.093
400 49 4.4
?
3 4.4 0.095
0.048
180 52 4.4
0.078
4 4.4 0.089
0.045
125 51 4.4
0.052
5 4.4 0.156
0.078
75 48 4.4
0.037
6 4.4 0.141
0.071
150 40 4.4
0.045
6 88.2
0.670
0.335
150 40 51.4
0.335
9 4.4 0.223
0.0004
6 80 4.4
0.156
10 4.4 0.112
0.112
200 27 4.4
0.074
12 4.4 0.019
0.187
150 150?
4.4
0.007
__________________________________________________________________________
.sup.1 All examples use solutions said adjusted to pH 1 with sulfuric
acid, except Ex. 12 in which no sulfuric acid is added and the pH is not
reported.
.sup.2 Reactor type: sg = shaking glass, ss = stainless steel (method of
agitation not reported)
.sup.3 Palladium concentration, millimolar (mgatom/liter)
.sup.4 Heteropolyacid concentration, Molar (gmole/liter)
.sup.5 Heteropolyacid said to be used, according to the formula H.sub.n
[PMo.sub.p V.sub.q O.sub.40 ], n = 3 + q, p = 12 - q
.sup.6 Vanadium used in excess in the preparation of the HPA solution, %
of q (see footnote 5)
.sup.7 Palladium turnover number per ethylene reaction = (C.sub.2 H.sub.4
capacity, moles/liter)/(Pd concentration, moles/liter)
.sup.8 Fraction of vanadium reduced (utilized to oxidize ethylene) in
ethylene reaction = (C.sub.2 H.sub.4 capacity, mole/l)/[(total V
concentration, gatom/l)/2], where total V concentration = [HPA](q)(1 +
fraction excess V used in HPA solution preparation)
.sup.9 Average rate of ethylene reaction as [(milliters C.sub.2 H.sub.4 a
750 mmHg, 23.degree. C.)/liter solution]/minute.
.sup.10 Average rate of oxygen reaction as [(milliters O.sub.2 at 750
mmHg, 23.degree. C.)/liter solution]/minute.
.sup.11 Rate of ethylene reaction as [millimoles C.sub.2 H.sub.4 /liter
solution]/second.
.sup.12 Palladium turnover frequency, {[millimoles C.sub.2 H.sub.4 /liter
solution]/second}/millimolar Pd concentration.
.sup.13 Rate of oxygen reaction as [millimoles O.sub.2 /liter
solution]/second.
One test in Example 6 is reported for another reactor, a stainless steel
reactor, with 88.2 psi of ethylene and with 51.4 psi of oxygen, each at
110.degree. C. The method of mixing the gas and liquid phases in this
reactor is not specified. Example 6 also reports results with the same
catalyst system in the shaking glass reactor. The ethylene reaction rates
were 0.141 (millimoles/liter)/second in the shaking glass reactor and
0.670 (millimoles/liter)/second in the stainless steel reactor. The oxygen
reaction rates were 0.045 (millimoles/liter)/second in the shaking glass
reactor and 0.335 (millimoles/liter)/second in the stainless steel
reactor. Thus, the reaction rates did not increase proportionally with the
pressure when it was increased from about 4 psi to about 90 psi. It is
well known that the diffusion rate of a reacting gas into a liquid, as
well as the gas molecule concentration in the liquid phase at saturation,
is proportional to the partial pressure of the gas in the gas phase, all
other factors being constant. Accordingly, the stainless steel reactor
used for the higher pressure test of Example 6 appears to be a poorer
device for the mixing of gas and liquid phases than the shaking glass
reactor used for the other tests in the Matveev patents.
Typical apparent palladium turnover frequencies calculated from ethylene
reaction rates and palladium concentrations reported in Matveev patents'
working examples using a shaking glass reactor are all less than 0.2
(millimoles C.sub.2 H.sub.4 /mg-atom Pd)/second. The higher pressure test
at 110.degree. C. in a stainless steel reactor in Example 6 gave the
highest apparent palladium turnover frequency of 0.335 (millimoles C.sub.2
H.sub.4 /mg-atom Pd)/second. Although Matveev patents purport that the
disclosed catalysts are up to 30 to 100 times more active in olefin
oxidation over the Wacker catalyst, the apparent activity of the palladium
catalyst in the best example is no higher than the activity of a typical
Wacker palladium catalyst in typical process operation at comparable
temperatures. This result is obtained even though the disclosed catalyst
solution is substantially free of the chloride ion concentration which
inhibits the palladium activity in the Wacker catalyst. In contrast, the
present invention demonstrably provides palladium catalyst activities
substantially exceeding the activity of a Wacker palladium catalyst in
typical process operation.
From Matveev patents' ethylene reaction capacities and the palladium
concentrations, the number of palladium turnovers per ethylene reaction
capacity can be calculated (see Table 1, TON). The highest number of
turnovers obtained was 400 with the heteropolyacid containing 8 vanadium
atoms (and with 35% excess vanadium present), Example 2.
The ethylene reaction capacities of the catalyst solutions of Matveev's
working examples appear generally to follow the vanadium content of the
solutions (see Table 1). For the tests with the preferred concentrations
of heteropolyacid and palladium and at the preferred "pH" 1 (Examples
1-6), the reported ethylene reaction capacities are calculated to
correspond to 40% to 53% of the oxidizing capacity of the vanadium(V)
content of the solution, assuming two vanadium(V) centers are reduced-to
vanadium(IV) for each ethylene oxidized to acetaldehyde.
Example 12 of Matveev's Belgian patent reports a test with no addition of
sulfuric acid. (This result was omitted from the UK patent.) The
heteropolyacid is designated H.sub.5 [PMo.sub.10 V.sub.2 O.sub.40 ] and is
used at 0.1 molar concentration with palladium sulfate at 0.1
mg-atom/liter concentration. A "pH" for this solution is not reported. The
reaction is conducted at 50 C. On cycling between ethylene and oxygen
reactions, the rate of the ethylene reaction is said to diminish
constantly due to hydrolysis of the Pd salt. (Typical examples with
sulfuric acid added, such as examples 1-6, were reported stable to 10 or
more cycles.) This result corresponds to Matveev's disclosure that the
stability of the catalyst is increased by sulfuric acid, that the amount
of acid is such as to maintain the "pH" at not more than 3, and that with
higher "pH" values the catalyst is not sufficiently stable against
hydrolysis and palladium precipitation. This result reported with no
addition of sulfuric acid is so poor as to lead one away from attempting
to use the example.
Matveev patents also report working examples for the oxidation of propylene
to acetone, n-butenes to methyl ethyl ketone, and 1-hexene to methyl butyl
ketone using the disclosed catalyst system. For reaction of mixtures of
n-butenes, 4.4 psi, at 90.degree. C. in the shaking glass reactor (Example
19 in Belgian 828,603; Example 16 in UK 1,508,331 ), the reported reaction
rate is 50 [(ml butenes at 750 mm Hg, 23.degree. C.)/liter]/minute
(corresponding to 0.037 (millimoles butenes/liter)/second) an the capacity
of the reaction solution is 0.25 moles butenes/liter. The palladium
concentration in the example is 2 mg-atom/liter: the palladium turnover
frequency is calculated 0.019 (millimoles butones/mg-atom Pd)/second; the
number of Pd turnovers per butene reaction capacity is calculated 125. The
fraction of the vanadium(V) concentration of the solution reduced by the
butone capacity is calculated 51%.
In contrast to the teachings of the Matveev patents, we have found the
following: 1) Although the Matveev patents teach that sulfuric acid
increases the activity and stability of the catalyst, we have discovered
that substantially increased activity (olefin and oxygen reaction rates)
and stability can be obtained by avoiding the presence of sulfuric acid,
and of sulfate species generally; 2) Although the Matveev patents teach
that the rate of the oxygen reaction is appreciably diminished at "pH"
values lower than 1, we have discovered that oxygen reaction rates can be
obtained which are orders of magnitude higher than those reported in the
patents end which are substantially undiminished in solutions having
hydrogen ion concentrations greater than 0.10 mole/liter; 3) Although the
Matveev patents teach that the activity and stability of the catalyst all
increased on increasing the number of vanadium atoms in the polyacid, for
example from 1 to 6, we have discovered that, at least in the practice of
the present inventions, the activity (olefin and dioxygen reaction rates)
is typically invariable with the vanadium content of the polyacid and the
stability may be decreased on increasing the vanadium content of the
polyacid towards 6; 4) Although the Matveev patents teach that the total
number of Na atoms per atom of P be not less than 6, we have found that
with the preferred polyoxoanion-comprising catalyst solutions of the
present invention, which optionally contain Na.sup.+ countercations, the
desired acidity can be obtained while avoiding sulfuric acid by preferably
keeping the number of Na atoms per atom of P less than 6.
East German Patent No. 123,085, by some of the inventors of the Matveev
patents, discloses a chloride-free catalyst for the liquid phase oxidation
of ethylene to acetaldehyde and acetic add that consists of a solution of
a palladium salt with an anion that does not complex palladium or does so
only weakly and a heteropolyacid or isopolyacid or salts thereof that have
a redox potential greater than 0.35 V. The aqueous solutions disclosed in
the Examples contain 2.5.times.10.sup.-4 mole/liter PdSO.sub.4,
5.times.10.sup.-2 mole/liter heteropolyacid, (specified as H.sub.5
[P(Mo.sub.2 O.sub.7).sub.5 V.sub.2 O.sub.6 ], H.sub.8 [Si(Mo.sub.2
O.sub.7)V.sub.2 O.sub.6 ], or H.sub.8 [Ge(Mo.sub.2 O.sub.7)V.sub.2
O.sub.6]), 5.times.10.sup.-2 mole/liter CuSO.sub.4 (omitted in Example 3),
and 5.times.10.sup.-2 mole/liter NaVO.sub.3, and are said to have a "pH"
of 2. Neither the method of preparation of the heteropolyacids in the
solutions, nor the means of acidifying the solutions to this stated "pH"
is disclosed. In the Examples, these solutions are said to be reacted at
30.degree. C. with ethylene at 720 mm Hg partial pressure or at 60.degree.
C. with ethylene at 600 mm Hg partial pressure, and with oxygen at the
same pressures, using a glass reactor that can be agitated. The greatest
ethylene reaction rate disclosed is 44 ml ethylene reacted by 50 ml
solution in 20 minutes at 60.degree. C. with an ethylene partial pressure
of 600 mm Hg, corresponding to 0.021 (millimole C.sub.2 H.sub.4
/liter)/second and a palladium turnover frequency of 0.085 (millimole
C.sub.2 H.sub.4 /mg-atom Pd)/second. The greatest oxygen reaction rate
disclosed is 10 ml oxygen reacted by 50 ml solution in 27 minutes at
30.degree. C. with an oxygen partial pressure of 720 mm Hg, corresponding
to 0.005 (millimole O.sub.2 /liter)/second.
East German Patent No. 123,085 also mentions small additions of chloride or
bromide ions act as oxidation accelerators and activate the catalysts,
with molar ratios of [Pd.sup.++ ]:[Cl.sup.- ].ltoreq.1:20 and [Pd.sup.++
]:[Br.sup.- ].ltoreq.1:5 being favorable. The patent makes no other
mention of chloride addition to the disclosed catalyst and chloride is
nowhere Indicated in any of the working Examples.. Instead, the title of
the patent, the claims, and the disclosure elsewhere all explicitly
specify a chloride-free catalyst.
Additional results from some of the inventors of the Matveev patents are
reported in Kinetika i Kataliz, vol. 18 (1977), pp. 380-386 (English
translation edition pp, 320-326, hereafter "Kinet. Katal. 18-1"). Reaction
kinetic experiments are reported for the ethylene oxidation reaction with
phosphomolybdicvanadic heteropolyacids in the presence of Pd(II) sulfate
using a shaking reactor with circulation of the gas phase. The absolute
values of the observed reaction rates are said to be quite small, and not
complicated by mass-transfer processes. Most of the reported experiments
are conducted at about 20.degree. C., and this low temperature appears to
be the principal reason the observed reaction rates are so small. Typical
reaction rates reported are about 1 to 12.times.10.sup.-4
(moles/liter)/minute, which corresponds to about 0.002 to 0.020
(millimoles/liter)/second; compare to ethylene reaction rates of about
0.1-0.2 (millimoles/liter)/second calculated from the results reported for
experiments at 90.degree. C. in Matveev patents (see Table 1). The
reaction rates reported in Kinet. Katal. 18-1 are so small as to lead one
away from attempting to use the reported reaction conditions for any
practical production purpose.
Ethylene pressures for the reactions of Kinet. Katal. 18-1 are not
reported. The ethylene concentrations are instead given, but no method of
either setting or determining the ethylene concentration is mentioned, nor
is it dear whether these ethylene concentrations are sustained in solution
under the reaction conditions.
Kinet. Katal. 18-1 states that solutions of phosphomolybdicvanadic
heteropolyacids were synthesized by a procedure described in Zh. Neorg.
Khim., vol. 18 (1973), p. 413 (English translation edition pp. 216-219).
This reference describes making solutions from Na.sub.2 HPO.sub.4,Na.sub.2
MoO.sub.4 .multidot.2H.sub.2 O, and NaVO.sub.3 .multidot.2H.sub.2 O at
"pH" 2; the method of acidification of the solutions of these basic salts,
when stated, is with sulfuric acid. (This reference further mentions the
isolation of crystalline vanadomolybdophosphoric acids via ether
extraction of their ether addition compounds from sulfuric acid-acidified
solutions. These methods of preparing solution vanadomolybdophosphoric
acids with sulfuric acid and crystalline products by ether extraction are
also described in earlier papers cited by this reference; for example,
Inorg. Chem., 7 (1968), p. 137.) The reaction solutions of Kinet. Katal.
18-1 are said to be prepared from the solutions of phosphomolybdicvanadic
heteropolyacids by addition palladium sulfate, dilution, and adjustment of
the "pH" by the addition of H.sub.2 SO.sub.4 or NaOH. However, this
reference does not disclose the composition of the test solutions, in
terms of the amounts of H.sub.2 SO.sub.4 or NaOH added, nor any method for
determining the "pH" of the disclosed solutions.
Kinet. Katal. 18-1 reports the dependence of the ethylene reaction rate on
the solution "pH" over the stated range 0.8 to 2.2, under the disclosed
conditions with the heteropolyacid designated H.sub.6 [PMo.sub.9 V.sub.3
O.sub.40 ] at 0.05 mole/liter, palladium at 3.times.10.sup.-3
g-atom/liter, ethylene at 1.times.10.sup.-4 mole/liter, and 21 C. As the
"pH" is increased towards 2, the rate of the ethylene reaction is shown to
decrease. From evaluation of graphic figures in the reference, the maximum
rate of ethylene reaction was achieved over a "pH" range of 0.8 to 1.6,
and corresponded to 0.023 (millimole C.sub.2 H.sub.4 /liter)/second and a
palladium turnover frequency of 0.078 (mole C.sub.2 H.sub.4 /mole
palladium)/second.
Matveev reviews his studies on the oxidation of ethylene to acetaldehyde in
Kinetika i Kataliz, vol. 18 (1977), pp. 862-877 (English translation
edition pp. 716-727; "Kinet. Katal. 18-2"). The author states (English
translation edition p. 722): "The chloride-free catalyst was an aqueous
solution of one of the HPA-n, acidified with H.sub.2 SO.sub.4 to "pH" 1,
in which a nonhalide palladium salt (sulfate, acetate, etc.) was
dissolved." (HPA-n are defined therein as phosphomolybdenumvanadium
heteropolyacids.) Reference is then made to the studies reported in Kinet.
Katal. 18-1.
Reaction Kinetics and Catalysis Letters, vol 16 (1981), pp. 383-386 reports
oxidation of 1-octane to 2-octanone using a catalytic system of PdSO.sub.4
and heteropolyacid designated H.sub.9 PMo.sub.6 V.sub.6 O.sub.40 in a
shaking glass reactor with 1 atm. oxygen. The heteropolyacid is said to be
synthesized as in UK 1,508,331, and used as an acidic sodium salt Na.sub.7
H.sub.2 PMo.sub.6 V.sub.6 O.sub.40. The catalyst solution is said to have
a "pH" equal to 0.5-1.0, which was attained by the addition of H.sub.2
SO.sub.4. However, no results are identified with any specific "pH" value.
Palladium is used in concentrations of .about.4-6 millimolar and
PdSO.sub.4 is said to give a more active catalyst than PdCl.sub.2. The
catalyst is said to have limited stability above 80.degree. C., apparently
due to precipitation of palladium.
Ropa Uhlie 28, pp. 297-302 (1986) (Chem Abstr. 107(1):6740r) reports
oxidation of 1-octene to 2-octanone using a solution of 0.075M
heteropolyacid designated H.sub.3+n PMo.sub.12-n V.sub.n O.sub.40, n=6 or
8, and containing PdSO.sub.4. The heteropolyacid solution was prepared
from NaH.sub.2 PO.sub.4, MoO.sub.3, and V.sub.2 O.sub.5 in water by
addition of NaOH, then H.sub.2 SO.sub.4, with adjustment of the stated
"pH" to 1.
J. Organomet. Chem. 327 (1987) pp. C9-C14 reports oxidation of 1-octene to
2-octanone by oxygen using an aqueous solution of 0.12 mole/liter
heteropolyacid designated HNa.sub.6 PMo.sub.8 V.sub.4 O.sub.40, with 0.01
mole/liter PdSO.sub.4, with various co-solvents, at 20.degree. C., in
one-stage mode. The heteropolyacid is said to be prepared by the method
described in UK 1,508,331; the "pH" of the catalyst solution is not
specifically disclosed. For the reaction, 1-octene and oxygen are
contacted simultaneously with the catalyst solution. The heteropolyacid
cocatalyst is said to be regenerated by treating the aqueous solution with
1 atm. O.sub.2 at 75.degree. C.
Reaction Kinetics and Catalysis Letters, vol 3 (1975), pp. 305-310 reports
the oxidation of vanadium(IV) in aqueous solutions of vanadyl sulfate
(V.sup.IV OSO.sub.4), 0.05-0,25 mole/liter, in the "pH" region 2.5-4.5, in
the presence of small amounts of sodium molybdate in a shaker reactor, at
30 C. with 730 mmHg oxygen pressure. At "pH" values below 3.0 the reaction
rate is reported to decrease sharply. A heteropolyacid complex of
molybdenum and vanadium was isolated from a reaction solution.
Koordinatsionnaya Khimiya, vol. 3 (1977), pp. 51-58 (English translation
edition pp. 39-44) reports the oxidation of reduced phosphomolybdovanadium
heteropolyacids containing vanadium(IV), in aqueous solution at "pH"'s>1,
at 60.degree. C. by oxygen. Heteropolyacids designated H.sub.3+n
[PMo.sub.12-n VnO.sub.40 ], n=1-3, were said to be synthesized by the
method of Zh. Neorg. Khim., vol. 18 (1973), p. 413 (see above), and a
solution of the sodium salt of the heteropolyacid designated n=6 was said
to be prepared by dissolving stoichiometric amounts of sodium phosphate,
molybdate, and vanadate in water, boiling the solution, and acidifying it
to "pH" 1. Different "pH" values for the solutions of the reduced forms of
these heteropolyacids were said to be obtained by altering the initial
"pH" values of the heteropolyacid solutions, monitored by a pH meter. The
acid used for acidification and for altering the initial "pH" values are
not disclosed. Oxygen reaction rates for the reduced forms of the
heteropolyacids designated n=2, 3, and 6 show maxima at about "pH" 3 (at
about 34.times.10.sup.-3 (mole/liter)/minute; or, 0.57
(millimole/liter)/second), and decline precipitously as the "pH" is
lowered; it becomes almost negligible for n=2 at "pH" 1.
Koordinatsionnaya Khimiya, vol. 5 (1979), pp. 78-85 (English translation
edition pp. 60-66) reports the oxidation of vanadium(IV) in aqueous
solutions of vanadyl sulfate, 0.1-0.4 mole/liter, in the "pH" region
2.5-4.5, in the presence of smaller amounts of molybdovanadophosphoric
heteropolyacid designated H.sub.9 PMo.sub.6 V.sub.6 O.sub.40, in an
agitated reactor, at 0.degree.-30.degree. C., by oxygen. A weak dependence
of the rate on "pH" is reported, with the rate decreasing with decreasing
"pH" below about "pH" 3.5. The addition of Na.sub.2 SO.sub.4 is said to
have no influence on the rate of the reaction.
Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, 1981, pp. 2428-2435
(English translation edition pp. 2001-2007) reports studies of the
oxidation of reduced forms ("blues") of molybdovanadophosphate
heteropolyacids designated H.sub.3+n [PMo.sub.12-n VnO.sub.40 ], n=1-4,6,
containing vanadium(IV), in aqueous solution at "pH" 3.0, in a glass flask
with magnetically-coupled stirring of the liquid phase, at 25.degree. C.
with 2-10 kPa (0.3-1.5 psi) oxygen. Reaction rates are extremely slow
under these low temperature, low pressure conditions in this reaction
mixing vessel. (From the data, reaction rates in the region <0.0001
(millimoles/liter)/ second are calculated.) The oxygen reaction rates of a
reduced form of the molybdovanadophosphate n=3 were measured at "pH"'s
2.0, 3.0, and 4.0. A maximum was observed at "pH" 3.0. Aqueous solutions
of Na salts of the heteropolyacids and the corresponding blues for the
experiments were said to be obtained as in Izvestiya Akademii Nauk SSSR,
Seriya Khimicheskaya, 1980, pp. 1469. This reference discloses that
aqueous solutions of heteropolyanions were obtained by reacting
stoichiometric amounts of H.sub.3 PO.sub.4, MoO.sub.3, and NaVO.sub.3
.multidot.2H.sub.2 O with heating in the presence of Na.sub.2 CO.sub.3.
(Neither the amount of Na.sub.2 CO.sub.3 added, the concentration of
heteropolyanion, the resulting "pH"'s, nor the complete compositions of
the solutions are disclosed.) This reference further discloses the
addition of vanadium(IV) in the form of VOSO.sub.4 .multidot.2H.sub.2 O to
produce the heteropoly blues. The experimental solutions in this reference
are said to comprise heteropolyanion and vanadyl at "pH" 1.60-2.98, buffer
solution of NaHSO.sub.4 and Na.sub.2 SO.sub.4 ; neither the concentration
of the buffering sulfate ions nor an accounting of their origin is
disclosed.
Reaction Kinetics and Catalysis Letters, vol 17 (1981), pp. 401-406 reports
the oxidation of vanadium(IV) in aqueous solutions of vanadyl sulfate,
0.02-0.4 mole/liter, in the "pH" region 2.5-4.5, in the presence of
smaller amounts of molybdovanadophosphoric heteropolyacid designated
H.sub.6 PMo.sub.9 V.sub.3 O.sub.40, by the methods of Koordinatsionnaya
Khimiya, vol. 5 (1979), pp. 78-85. At "pH" values below 3.0 the reaction
rate is reported to decrease sharply.
J. Chem. Soc. Dalton Trans., 1984, pp. 1223-1228 reports studies of the
palladium sulfate-catalyzed oxidation of 1-butene to 2-butanone (methyl
ethyl ketone) with phosphomolybdovanadic acids both in the absence and in
the presence of oxygen. These studies are reported in greater detail in
Palladium and Heteropolyacid Catalyzed Oxidation of Butene to Butanone, S.
F. Davison, Ph.D. Thesis, University of Sheffield, 1981. These references
report, as do others Ioc. cit., that phosphomolybdovanadic acids are
extremely complex mixtures of anions of the type [PMo.sub.12-x V.sub.x
O.sub.40 ].sup.(3+x)-. Crystalline phosphomolybdovanadic acids, designated
H.sub.3+n [PMo.sub.12-n VnO.sub.40 ], n=1-3, prepared by the ether
extraction method of Inorg. Chem., 7 (1988), p. 137 were observed to be
mixtures which disproportionated still further in the acidic media used
for catalysis. Accordingly, solutions prepared by the method of UK
1,508,331 were chosen as appropriate for the catalytic reactions (see
Davison Thesis, pp. 63 and 77), except that stoichiometric amounts of
V.sub.2 O.sub.5 (not excess) were used. The solutions were prepared from
V.sub.2 O.sub.5, MoO.sub.3, Na.sub.3 PO.sub.4 .multidot.12.sub.2 O, and
Na.sub.2 CO.sub.3, at 0.2M P, and acidified to "pH" 1 by addition of
concentrated sulfuric acid.
The reactions of J. Chem. Soc. Dalton Trans., 1984, pp. 1223-1228 and
Davison Thesis in the absence of oxygen were conducted at 20.degree. C.
and 1 atm 1-butene in a mechanically shaken round-bottomed flask.
Reactions using 5 mM PdSO.sub.4 and 0.05M vanadium(V) in aqueous sulfuric
acid (0.03-0.2 mole/liter, depending on n) are reported to give similar
initial reaction rates for n=1-7. The reactions required ca. 30 minutes
for completion and gave 5 turnovers on Pd (stoichiometric for two
vanadium(V) reduced to vanadium(IV) per 1-butene oxidized to 2-butanone.).
A stated intention of the work was to minimize chloride content;
PdCl.sub.2 is said to have similar reactivity to PdSO.sub.4.
The reactions of J. Chem. Soc. Dalton Trans., 1984, pp. 1223-1228 and
Davison Thesis in the presence of oxygen were conducted at 20.degree. C.
and 1 atm of 1:1 1-butene:oxygen in a round-bottomed flask with
magnetically coupled stirring. Results are reported for the solutions used
in reactions in the absence of oxygen; up to about 40 turnovers on Pd were
obtained in about 120 minutes with the heteropolyacid designated PMo.sub.6
V.sub.6 (H.sub.9 [PMo.sub.6 V.sub.6 O.sub.40 ] in the journal account). An
experiment is also reported using this heteropolyacid in 0.87M sulfuric
acid (in the journal account it is cited as 1M sulfuric acid and the "pH"
is stated to be ca. -0.3.). The extra acid is said to be slightly
detrimental: up to about 32 turnovers on Pd were obtained in about 120
minutes. The various P-Mo-V co-catalysts are said to be longer lasting in
the "pH" range 1-2.
U.S. Pat. Nos. 4,434,082; 4,448,892; 4,507,506; 4,507,507; 4,532,362; and
4,550,212, assigned to Phillips Petroleum Company, disclose systems for
oxidizing olefins to carbonyl compounds comprising a palladium component,
a heteropolyacid component, and additional components. U.S. Pat. Nos.
4,434,082 and 4,507,507 both add a surfactant and a diluent of two liquid
phases, one of which is an aqueous phase, and one of which is an organic
phase. U.S. Pat. Nos. 4,448,892 and 4,532,362 also both add a surfactant
and a fluorocarbon. U.S. Pat. No. 4,507,506 adds cyclic sulfones (e.g.
sulfolane). U.S. Pat. No. 4,550,212 adds boric acid and optionally a
surfactant. The disclosure of heteropolyacids in each of these patents is
the same as in Matveev patents, and the heteropolyacids demonstrated by
working examples are prepared by the same method as in Matveev patents,
including acidification to "pH" 1.00 with sulfuric acid. PdCl.sub.2 is
among the palladium components exemplified. Among the disclosed
surfactants are quaternary ammonium salts and alkyl pyridinium salts,
including chloride salts. However, cetyltrimethylammonium bromide is the
only surfactant demonstrated by working example.
The working examples for olefin oxidation among the above patents
predominantly demonstrate the one-stage oxidation of individual n-butenes
to 2-butanone in the presence of oxygen. U.S. Pat. Nos. 4,434,082 and
4,507,507 demonstrate oxidation of 3,3-dimethyl-1-butene and
3-methyl-1-butene. U.S. Pat. Nos. 4,448,892 and 4,532,362 demonstrate the
oxidation of 1-dodecene. U.S. Pat. No. 4,507,506 is concerned with the
one-stage oxidation of long-chain alpha-olefins and demonstrates
oxidations of 1-decene and 1-dodecene.
U.S. Pat. Nos. 4,720,474 and 4,723,041, assigned to Catalytica Associates,
disclose systems for oxidizing olefins to carbonyl products comprising a
palladium component, a polyoxoanion component, and additionally a redox
active metal component (certain copper, iron, and manganese salts are
disclosed) and/or a nitrile ligand. The disclosures emphasize the
elimination of chloride from the system; the catalyst systems do not
contain chloride ions except sometimes as "only trace amounts" resulting
from the presence of chloride in the synthesis of the polyoxoanion "in
order to form and (or) crystallize the desired structure". The patents
disclose that "pH" or acidity can be adjusted by various proton sources,
such as an acid form of a polyoxoanion or certain inorganic acids;
sulfuric acid is said to be a preferred acid and is the only acid so
described. The "pH" of the liquid phase is said to be preferably
maintained between 1 and 3 by the addition of appropriate amounts of
H.sub.2 SO.sub.4. The working examples for olefin oxidation all add
H.sub.2 SO.sub.4 to the reaction solution, either to obtain 0.1N
concentration or to obtain "pH" 1.5 or 1.6.
U.S. Pat. Nos. 4,720,474 and 4,723,041 demonstrate by working example the
oxidation of various olefins to carbonyl products: predominantly 1-hexene,
as well as ethylene, 1- and 2-butenes, 4-methyl-1-pentene, cyclohexene,
1-octene, and 2-octene, all in the presence of oxygen. Example XL gives
initial olefin reaction rates using a catalyst solution including
Pd(NO.sub.3).sub.2, K.sub.5 H.sub.4 PMo.sub.6 V.sub.6 O.sub.40, and
Cu(NO.sub.3).sub.2, with H.sub.2 SO.sub.4 added to "pH" 1.5, at 85.degree.
C. and 100 psig total pressure with oxygen in a stirred reactor without
baffles. The reported ethylene reaction rate is 8.58.times.10.sup.-7 moles
C.sub.2 H.sub.4 /sec ml (0.858 (millimoles/liter)/second). This
corresponds to a palladium turnover frequency of 0.17 (millimoles C.sub.2
H.sub.4 /millimole Pd)/second. A slightly lower rate is reported for
1-butene.
OBJECTS OF THE INVENTION
The present invention is directed towards one or more of the following
objects. It is not intended that every embodiment will provide all these
recited objects. Other objects and advantages will become apparent from a
careful reading of this specification.
An object of this invention is to provide an effective and efficient
process for oxidation of an olefin to a carbonyl compound. Another object
of this invention is to provide a catalyst solution for oxidation of an
olefin to a carbonyl compound. Another object of this invention is to
provide an effective and efficient process for the preparation of catalyst
solutions for oxidation of an olefin to a carbonyl compound.
A further object of this invention is to provide an effective and efficient
process for oxidation of an olefin to a carbonyl compound by one or more
polyoxoanion oxidants in aqueous solution, catalyzed by palladium. Another
object of this invention is to provide an effective and efficient process
for reoxidation of one or more reduced polyoxoanions in aqueous solution
by reaction with dioxygen. Another object of this invention is to provide
an effective and efficient process for oxidation of an olefin to carbonyl
compound by dioxygen catalyzed by palladium and one or more polyoxoanion
in aqueous solution.
A further object of this invention is to provide an economically
practicable catalyst solution and process for oxidation of ethylene to
acetaldehyde in an industrial acetaldehyde plant designed to operate the
Wacker process chemistry. Another object of this invention is to provide
an economically practicable process for oxidation of an olefin, other than
ethylene, to a ketone in an industrial plant originally designed to
operate the Wacker process chemistry for the production of acetaldehyde.
A further object of this invention is to provide an economically
practicable catalyst solution and process for oxidation of an olefin
directly to a carbonyl compound, which could not be so accomplished
previously due to co-production of chlorinated by-products, due to
reaction rates which were too slow, or due to another reason.
A further object of this invention is to achieve any of the above
objectives with a less corrosive catalyst solution than the Wacker
catalyst solution. Another object of this invention is to achieve any of
above objectives while minimizing or avoiding the co-production of
hygienically or environmentally objectionable chlorinated organic
by-products. Another object of this invention is to achieve any of the
above objectives in the essential absence of copper chlorides.
A further object of this invention is to achieve any of the above
objectives with a higher volumetric productivity (molar amount of olefin
oxidized to carbonyl product per unit volume catalyst solution per unit
time) than previously disclosed catalyst systems and processes. A further
object of this invention is to achieve any of the above objectives with a
smaller concentration or amount of palladium catalyst than previously
disclosed catalyst systems and processes. Another object of this invention
is to achieve any of the above objectives with greater turnovers on
palladium (lesser Pd cost per mole carbonyl product) than previously
disclosed catalyst systems and processes. Another object of this invention
is to achieve any of the above objectives with greater catalyst stability
to long term operation than previously disclosed catalyst systems and
processes which avoid the use of copper chlorides. Another object of this
invention is to achieve any of the above objectives while avoiding the
inverse squared rate inhibition by chloride ion concentration and the
inverse rate inhibition by hydrogen ion concentration which are typical of
the Wacker chemistry.
A further object of this invention is to achieve any of the above
objectives with a greater effective utilization of the oxidation capacity
of a vanadium(V)-containing polyoxoanion oxidant solution, or greater
olefin reaction capacity per unit volume, than previously disclosed
catalyst systems and processes. Another object of this invention is to
achieve any of the above objectives with a greater volumetric reaction
rate for the oxidation of vanadium(IV) to vanadium(V) by dioxygen (molar
amount of dioxygen reacted per unit volume catalyst solution per unit
time) than previously disclosed vanadium-containing catalyst systems and
processes. A further object of this invention is to provide an effective
and efficient process for oxidation of palladium(0), particularly
palladium metal, to dissolved palladium(II) catalyst, in order to provide
and sustain palladium catalyst activity in the inventive catalyst system.
Still another object of this invention is to provide a method of preparing
an aqueous catalyst solution suitable for accomplishing any of the above
objectives.
SUMMARY OF INVENTION
The present invention provides aqueous catalyst solutions useful for
oxidation of olefins to carbonyl products, comprising a palladium catalyst
and a polyoxoacid or polyoxoanion oxidant comprising vanadium. It also
provides processes for oxidation of olefins to carbonyl products,
comprising contacting olefin with the aqueous catalyst solutions of the
present invention. It also provides processes for oxidation of olefins to
carbonyl products by dioxygen, comprising contacting olefin with the
aqueous catalyst solutions of the present invention, and further
comprising contacting dioxygen with the aqueous catalyst solutions.
In certain aqueous catalyst solutions and related processes of the present
invention, the solution has a hydrogen ion concentration greater than 0.10
mole per liter when essentially all of the oxidant is in its oxidized
state.
In other aqueous catalyst solutions and related processes of the present
invention, the solution is essentially free of mineral acids and acid
anions other than of the polyoxoacid oxidant and hydrohalic acids. In
other aqueous catalyst solutions and related processes of the present
invention, the solution is essentially free of sulfuric acid and sulfate
ions.
In other aqueous catalyst solutions and related processes of the present
invention, the solution further comprises dissolved olefin at a
concentration effective for oxidizing the olefin at a rate which is
independent of the dissolved olefin concentration. In other aqueous
catalyst solutions and related processes of the present invention, the
aqueous catalyst solution further comprises the olefin dissolved at a
concentration effective for maintaining the activity and stability of the
palladium catalyst for continued process operation.
In other aqueous catalyst solutions and related processes of the present
invention, the solution further comprises dissolved olefin at a
concentration effective for oxidizing the olefin at a rate of at least 1
(millimole olefin/liter solution)/second. In other processes of the
present invention, the process comprises contacting the olefin with an
aqueous catalyst solution, comprising a palladium catalyst and a
polyoxoacid or polyoxoanion oxidant, in mixing conditions sufficient for
the olefin oxidation rate to be governed by the chemical kinetics of the
catalytic reaction and not be limited by the rate of olefin dissolution
(mass transfer) into the solution. In other aqueous catalyst solutions and
related processes of the present invention, the aqueous catalyst solution
further comprises the olefin dissolved at a concentration effective for
the olefin oxidation rate to be proportional to the concentration of the
palladium catalyst. In other aqueous catalyst solutions and related
processes of the present invention, the aqueous catalyst solution further
comprises the olefin dissolved at a concentration effective for providing
a palladium turnover frequency of at least 1 (mole olefin/mole
palladium)/second. In other aqueous catalyst solutions and related
processes of the present invention, the solution further comprises
dissolved olefin at a concentration effective for oxidizing the olefin at
a rate which is independent of the dissolved olefin concentration. In
other aqueous catalyst solutions and related processes of the present
invention, the aqueous catalyst solution further comprises the olefin
dissolved at a concentration effective for maintaining the activity and
stability of the palladium catalyst for continued process operation.
In other aqueous catalyst solutions and related processes of the present
invention, the solution further comprises chloride ions. In other aqueous
catalyst solutions and related processes of the present invention, the
solution further comprises chloride ions at a concentration effective for
maintaining the activity and stability of the palladium catalyst for
continued process operation. In other aqueous catalyst solutions and
related processes of the present invention, the solution further comprises
chloride ions at a concentration greater than twice the concentration of
palladium. In other aqueous catalyst solutions and related processes of
the present invention, the solution further comprises chloride ions at a
concentration of at least 5 millimole per liter.
Preferred aqueous catalyst solutions and related olefin oxidation processes
of the present invention combine the recited features of two or more of
the above mentioned catalyst solutions and related processes. Especially
preferred are aqueous catalyst solutions and related processes which
combine most or all of the above features.
The present invention also provides processes for the oxidation of
vanadium(IV) to vanadium(V) comprising contacting dioxygen with an aqueous
solution comprising vanadium and a polyoxoanion. In certain such processes
of the present invention the solution has a hydrogen ion concentration
greater than 0.10 mole per liter when essentially all of the oxidant is in
its oxidized state. In other such processes of the present invention the
solution is essentially free of sulfate ions. In other such processes of
the present invention the dioxygen is mixed with the aqueous solution
under mixing conditions effective to provide a dioxygen reaction rate of
at least 1 (millimole dioxygen/liter solution)/second.
The present invention also provides processes for the oxidation of
palladium(0) to palladium(II) comprising contacting the palladium(0) with
an aqueous solution comprising a polyoxoacid or polyoxoanion oxidant
comprising vanadium and chloride ions. In certain such processes of the
present invention the palladium(0) comprises palladium metal or colloids.
The present invention also provides processes for the preparation of acidic
aqueous solutions of salts of polyoxoanions comprising vanadium, by
dissolving oxides, oxoacids, and/or oxoanion salts of the component
elements (for example: phosphorus, molybdenum, and vanadium), and
optionally carbonate, bicarbonate, hydroxide and/or oxide salts, in water,
such that the resulting ratio of hydrogen ions and salt countercations
balancing the negative charge of the resulting polyoxoanions in the
solution provides a hydrogen ion concentration greater than 10.sup.-5
moles/liter.
We anticipate that the solutions and processes of the present invention
will prove useful in oxidation processes other than the oxidation of
olefins to carbonyl compounds, including, for example, oxidation of carbon
monoxide, oxidation of aromatic compounds, oxidative coupling reactions,
oxidative carbonylation reactions, oxidation of halides to halogen, and
the like.
DETAILED DESCRIPTION OF THE INVENTION
Empirical and Theoretical Bases for the Invention
We have found after extensive investigations that certain catalyst
solutions and processes discussed in the background references are wholly
impractical or practically unworkable for economically practicable
commercial manufacture of carbonyl products by the oxidation of olefins.
Characteristic problems we found for background catalyst solutions and
processes using palladium and polyoxoanions include insufficient olefin
oxidation reaction rates, insufficient palladium catalyst activity,
insufficient catalyst stability for continued process operation, and
insufficient dioxygen reaction rates. The following discussion outlines
the results of our investigations towards solving these problems and our
understanding of why our solutions to these problems are successful. We do
not intend to be bound by the following theoretical explanations since
they are offered only as our best beliefs in furthering this art.
In the oxidation of olefins to carbonyl compounds by palladium catalysts
and polyoxoanion oxidants comprising vanadium, palladium appears to
catalyze the oxidation of olefins by vanadium(V) in the polyoxoanion
oxidant (illustrated in reaction (12) for ethylene oxidation to
acetaldehyde), where [V.sup.V ] and [V.sup.IV ] represent a single
vanadium(V) atom and single vanadium(IV) atom in an aqueous solution of
polyoxoanion oxidant, respectively:
##STR3##
In a subsequent step, conducted either simultaneously (one-stage process)
or sequentially (two-stage process) to the above, vanadium(IV) in the
polyoxoanion solution can be oxidized by dioxygen to regenerate
vanadium(V) for the oxidation of additional olefin:
2[V.sup.IV ]+2 H.sup.+ +1/2O.sub.2 .fwdarw.2[V.sup.V ]+H.sub.2 O (13)
(Reactions (12) and (13) combined give the overall reaction (1) for
oxidation of ethylene to acetaldehyde by dioxygen.)
Palladium appears to catalyze the oxidation of olefins by vanadium(V) in
the polyoxoanion oxidant (reaction (12)) by oxidizing the olefin (reaction
(14), illustrated for ethylene), and then reducing vanadium(V) (reaction
(15)):
C.sub.2 H.sub.4 +Pd.sup.II +H.sub.2 O.fwdarw.CH.sub.3 CHO+Pd.sup.0
+2H.sup.+( 14)
Pd.sup.0 +2[V.sup.V ].fwdarw.Pd.sup.II +2[V.sup.IV ] (15)
Functionally, the vanadium in the polyoxoanion solution mediates the
indirect oxidation of the reduced Pd.sup.0 by dioxygen (reaction (15) plus
reaction (13)), and functions in a manner similar to copper chloride in
the Wacker process. We have determined that, in preferred processes of the
present invention, under mixing conditions sufficient for the olefin
oxidation rate to be governed by chemical kinetics (not limited by the
kinetics of olefin dissolution into the solution), the volumetric rate of
olefin oxidation by aqueous polyoxoanion comprising vanadium(V) (reaction
(12))is first-order dependent on (proportional to) the concentration of
palladium(II), and is substantially independent of the concentration
vanadium(V). Accordingly, the oxidation of the Pd.sup.0 product of
reaction (14) by vanadium(V) (reaction (15)) is rapid relative to the rate
of olefin oxidation by palladium(II) (reaction (14)).
We discovered that the catalyst systems of the background references
discussed above become deactivated with agglomeration of Pd.sup.0 to
colloidal palladium or even to precipitated solid palladium metal. Such
agglomeration and precipitation competes with the oxidation of Pd.sup.0 by
vanadium(V) to regenerate the olefin-active Pd.sup.II form (reaction
(15)). Accordingly, what would have been an originally active palladium
inventory would progressively accumulate into an inactive form. For olefin
oxidation in the absence of dioxygen (as in equation (12)), essentially
complete palladium catalyst deactivation would often occur in these
referenced processes before effective utilization of the oxidizing
capacity of the vanadium(V) content of the solution. Even when most of the
palladium would remain active through the olefin reaction in two-stage
operation with subsequent dioxygen reaction, multiple olefin/oxygen
reaction cycles resulted in a cumulative loss of the active palladium
catalyst concentration.
The aqueous catalyst solutions of this invention have increased stability
towards deactivation because of palladium colloid or solid metal
formation. Apparently, our processes more rapidly oxidize Pd.sup.0 with
vanadium(V) (reaction (15)) in competition with agglomeration of Pd.sup.0
into colloids or solid palladium metal, and/or they aggressively oxidize
already agglomerated palladium(0) forms with vanadium(V), with the result
that the concentration of olefin-active Pd.sup.II is maintained. Among
features of the inventive solutions and related processes which contribute
to the increased stability are the following: 1) hydrogen ion
concentrations greater than 0.10 mole/liter, 2) presence of chloride ions,
especially when above a concentration coincidental to using PdCl.sub.2 as
the palladium source, 3) concentrations of dissolved olefin effective for
rapid reaction rates and sustained palladium catalyst activity, and 4)
essential absence of sulfate ions.
The favorable influences of hydrogen ion and chloride ion concentrations on
catalyst stability are thought to be related, in part, to decreasing
palladium 0/II oxidation potentials, favoring oxidation of all forms of
reduced palladium to active Pd.sup.II. We have also discovered that
chloride ion catalyzes the corrosive oxidation of even solid palladium
metal to soluble Pd.sup.II catalyst by polyoxoanions comprising
vanadium(V). Accordingly, chloride ions can function to disfavor net
accumulation of inactive colloidal and solid metallic palladium by
catalyzing rapid regeneration of all forms of palladium(0) to active
Pd.sup.II catalyst. A theoretical explanation for the favorable influence
of dissolved olefin concentration on palladium catalyst stability is that
dissolved olefin is able to bind to the Pd.sup.0 product of olefin
oxidation, stabilizing it in solution and thereby slowing its rate of
agglomeration into colloidal or metallic forms. The oft-used sulfate salts
may decrease ("salt-out") olefin solubility in the aqueous solution,
thereby decreasing its ability to stabilize the palladium catalyst.
In any event, we have found that, when the concentration of chloride ions
in the solution is insufficient to otherwise maintain palladium activity,
when ethylene concentration in solution is reduced (due to low ethylene
pressure in the gas phase and/or due to insufficient mixing of the gas and
liquid phases such that the ethylene oxidation rate becomes limited by the
rate of ethylene dissolution into the solution), initial palladium
activity declines precipitously. We have determined that such conditions
are typical of the examples disclosed in Matveev patents, and contribute
to their low apparent palladium catalyst activities relative to the
present invention; a significant fraction of the loaded palladium appears
to reside in inactive forms.
Effective concentrations of dissolved olefin for sustaining the palladium
activity may be achieved when the olefin is contacted with the aqueous
catalyst solution in mixing conditions sufficient for the olefin oxidation
rate to be governed by the chemical kinetics of catalysis (not limited by
the rate of ethylene diffusion into the solution), and are further
enhanced by raising the concentration of olefin in the olefinic phase (as
in raising the partial pressure of gaseous olefins). Mixing conditions
sufficient for the olefin oxidation rate to be governed by the chemical
kinetics of the catalytic reaction are established when the reaction rate
is governed by chemical characteristics of the catalyst solution, such as
its palladium(II) catalyst concentration, and independent of moderate
variations in the phase mixing efficiency. When mixing conditions are
insufficient, the dissolved olefin concentration in the bulk catalyst
solution is depleted by reaction, and the olefin oxidation rate becomes
determined by the rate of dissolution (mass transfer) of the olefin into
the catalyst solution. When mixing conditions are sufficient, the
dissolved olefin concentration approaches the phase partitioning limit
(the solubility of the olefin in the solution) and this limit is increased
in proportion to the olefin concentration in the olefinic phase. For each
combination of olefin, olefin concentration in the olefinic phase, precise
catalyst solution composition, and reaction temperature, sufficient mixing
requirements in a given reactor device can be established by observing
reaction rates governed by chemical kinetic parameters. For ethylene, with
preferred aqueous catalysts of the present invention, the ethylene
oxidation reactor of a Wacker plant, operated at its typical pressure and
temperature provides sufficient concentrations of dissolved ethylene.
In comparison to the inventive catalyst solutions and processes, the
catalyst systems and processes of background references using catalysts
comprising palladium and polyoxoanion components have generally poor
palladium catalyst activity. The background references typically utilize
much higher high palladium catalyst loadings to compensate for low
palladium activity, and even then do not report acceptable volumetric
olefin oxidation rates. A higher palladium concentration results in a
lesser number of palladium turnovers (moles olefin reacted/mole palladium
present) to react an amount of olefin. Accordingly, the palladium in the
systems of the background references is used relatively inefficiently;
that is, more palladium is used for the production of a given amount of
carbonyl product. Since palladium is a very costly catalyst solution
component, this places an economic burden on commercial utilization of the
background reference processes.
A convenient measure of palladium catalyst activity is the palladium
turnover frequency, (moles olefin reacted/mole palladium)/unit time.
Palladium turnover frequencies for ethylene oxidation determined from data
presented in the background references, are substantially less than 1
(mole ethylene/mole Pd)/second, often less than 0.1 (mole ethylene/mole
Pd)/second. Aqueous catalyst solutions and processes of the present
invention can provide palladium turnover frequencies greater than 1 (mole
ethylene/mole Pd)/second, generally greater than 10 (mole ethylene/mole
Pd)/second. Palladium turnover frequencies greater than 100 (mole
ethylene/mole Pd)/second have even been achieved with the present
invention.
Similarly improved palladium catalyst activities are also obtained for
olefins other than ethylene. Each olefin will have its own intrinsic rate
of reaction with the Pd.sup.II in a given aqueous catalyst solution, and
these rates are influenced by the conditions of the olefin oxidation
process using the solution. However, the relative reaction rates of
different olefins with various palladium catalyst solutions under various
reaction conditions generally follow the same qualitative order.
The poor palladium catalyst activity of the catalyst systems of the
background references can be attributed in part to the extent of
deactivation of the active palladium catalyst into inactive forms; a
fraction of the palladium load resides in colloidal or solid metallic
forms with little or no activity. To that extent, the features of the
catalyst solutions and related processes of the present invention which
contribute to improved palladium catalyst stability, as recited above,
also contribute to better apparent palladium catalyst activity.
Aqueous catalyst solutions and related processes of the present invention
were also discovered to provide higher intrinsic palladium(Ill activity
than the catalyst systems and processes of background references.
(Intrinsic palladium(Ill activity can be determined by observing initial
reaction rates under conditions when all the palladium loaded is initially
present as olefin-active palladium(Ill; that is, in the absence of any
accumulation of inactive forms.) Among the features of the inventive
solutions and related processes which contribute to increased intrinsic
palladium(II) activity are: 1) hydrogen ion concentrations greater than
0.10 mole/liter, 2) mixing conditions sufficient for the olefin oxidation
rate to be governed by the chemical kinetics of the catalysis, not limited
by the rate of olefin dissolution into the solution, 3) increased
concentrations of dissolved olefin in solution provided by increasing its
solubility (for example, by increasing the pressure of gaseous olefins),
and 4) essential absence of sulfate ions. Surprisingly, the presence of
chloride ions may also contribute to higher palladium activity, depending
on the chloride concentration and the hydrogen ion concentration.
Particularly, at hydrogen ion concentrations less than about 0.10
moles/liter, the presence of an effective concentration of chloride ions
can increase palladium activity over the level with no chloride present.
In acidic aqueous solutions comprising palladium(II) (containing no
coordinating ligands or anions other than water), Pd.sup.II exists in
aqueous solution predominantly as its hydrolytic forms: tetraaquopalladium
dication, Pd(H.sub.2 O).sub.4.sup.2+, aquated palladium hydroxide,
Pd(OH).sub.2 (H.sub.2 O).sub.2 and solid phase palladium oxide which may
be hydrated. These forms are interconverted by the following equilibria:
Pd.sup.II (H.sub.2 O).sub.4.sup.2+ .revreaction.Pd.sup.II (OH).sub.2
(H.sub.2 O).sub.2 +2H.sup.+ ( 16)
Pd.sup.II (OH).sub.2 (H.sub.2 O).sub.2 .revreaction.Pd.sup.II
O.multidot.nH.sub.2 O+(3-n)H.sub.2 O (17)
The two step-wise acid dissociation constants of reaction 16 have not been
resolved (Pd.sup.II (OH)(H.sub.2 O).sub.3.sup.+ has not been detected),
and the pK.sub.a of reaction 16, as written, is reported to be 2 in water,
at or near zero ionic strength.
We have found that, contrary to the teaching of Matveev patents, the
activity of the catalyst solution, specifically its volumetric olefin
oxidation reaction rate, is independent of the vanadium content of
phosphomolybdovanadate heteropolyacids, when tested at the same hydrogen
ion concentration greater than 0.10 mole/liter, in the absence of sulfuric
acid and sulfate ions, under mixing conditions sufficient for the rate to
be governed by the chemical kinetics of catalysis. Since the chemical
kinetics are first-order dependent on the concentration of the Pd.sup.II,
these findings indicate that under these conditions, the olefin-active
Pd.sup.II is not coordinated by phosphomolybdovanadate neteropolyanions
(since its reactivity does not depend on the identity of
heteropolyanions). Accordingly, it appears that under these conditions,
the olefin-active Pd.sup.II exists in solution as tetraaquopalladium,
Pd.sup.II (H.sub.2 O).sub.4.sup.2+.
We further discovered that (in the effective absence of chloride ion) the
rate of palladium catalyzed olefin oxidation in the polyoxoanion solution
is highest with solutions having hydrogen ion concentrations greater than
0.1 mole/liter, and rates decrease substantially as the hydrogen ion
concentration of the solution is decreased to 0.1 mole/liter and less.
This indicates that the dicationic tetraaquopalladium, Pd.sup.II (H.sub.2
O).sub.4.sup.2+ is the most active form of palladium(II) under these
conditions, and that as the hydrogen ion concentration of the solution is
decreased to 0.1 mole/liter and less, an increasing fraction of the
palladium(II) present as Pd.sup.II (H.sub.2 O).sub.4.sup.2+ is converted
to less active (lower positively charged and less electrophilic) hydroxo-
and/or oxo-forms by deprotonation of coordinated water, via equilibria
such as reactions (16) and (17). These hydrolytic forms are apparently
less active due to their lower positive charge and decreased
electrophilicity at Pd.sup.II. Therefore, it is quite desirable to utilize
polyoxoanion solutions having hydrogen ion concentrations greater than
0.10 mole/liter.
Hydrogen ion concentrations of polyoxoanion solutions, as recited herein,
refer to the hydrogen ion concentration when essentially all the
polyoxoanion is fully oxidized, which is when essentially all the vanadium
is vanadium(V). The hydrogen ion concentrations of preferred polyoxoanion
solutions often change when they are reduced, and these changes are not
yet completely understood and predictable. Some solutions having hydrogen
ion concentrations greater than 0.10 mole/liter when fully oxidized were
discovered to have hydrogen ion concentrations less than even 0.01
mole/liter after being fully reduced by olefin oxidation. Since the
theoretical equation for olefin oxidation (reaction (12)) potentially adds
hydrogen ions into solution, the decreased hydrogen ion concentration in
these reduced solutions presumably results from some re-equilbration of
the initially produced vanadium(IV)-polyoxoanion species with water which
consumes even more hydrogen ions than are potentially released by reaction
(12).
None-the-less, olefin oxidation reactions using such an oxidized solution
were found to proceed with an essentially constant rate characteristic of
the initial hydrogen ion concentration up to high conversion of the
vanadium(V) when provided with a sufficient combination of palladium
concentration, dissolved olefin concentration, temperature, and other
reaction conditions to achieve a relatively rapid olefin reaction. In
contrast, when the reaction conditions were not sufficient to provide such
a relatively rapid olefin reaction, the reaction rate would decelerate
with vanadium(V) conversion, commensurate with a concomitant decrease in
hydrogen ion concentration. Apparently, when sufficient reaction
conditions are provided for relatively rapid olefin reaction, high
vanadium(V) conversion occurs before a significant decrease in hydrogen
ion concentration can occur by what must be relatively slow
re-equilbration of the initially produced vanadium(IV)-polyoxoanions. In
contrast, when the reaction conditions are not sufficient to provide
relatively rapid olefin reaction, this slow re-equilbration of the
initially produced vanadium(IV)-polyoxoanions can occur while they are
relatively slowly formed and the reaction rate decelerates concomitant
with the decreasing hydrogen ion concentration.
Background references for the oxidation of olefins with systems using
palladium and vanadium-containing polyoxoacids generally teach that
PdCl.sub.2 and PdSO.sub.4 are equivalent palladium catalysts. PdSO.sub.4
completely ionically dissociates in water to sulfate ions and one or more
hydrolytic forms of Pd.sup.II, as governed by hydrogen ion concentration.
Accordingly, one would be led to conclude that when PdCl.sub.2 is added in
the systems of the background references, chloride is similarly
dissociated to give the same hydrolytic form(s) of Pd.sup.II. However, the
background references do not report the addition of chloride ions at a
concentrations in excess of that coincidental to providing PdCl.sub.2.
Indeed, the background references generally promote that chloride-free
systems are most desirable. The Wacker system, with its higher
concentrations of chloride, typically about 2 moles/liter, exhibits a
severe, second order inhibition of the ethylene oxidation rate by chloride
ion concentration.
Inventive aqueous catalyst solutions and related processes, by having an
effective concentration of chloride ions, give substantially improved
catalyst stability with little to only moderate inhibition of the
intrinsic Pd.sup.II activity. Moreover, since a greater fraction of loaded
palladium can be maintained in the active Pd.sup.II form, greater
productivity can be obtained from the total palladium load in continuous
operation by the addition of an effective concentration of chloride ions.
In tested embodiments with hydrogen ion concentrations less that 0.1
mole/liter, the presence of chloride ion at 5 millimoles/liter does not
inhibit Pd.sup.II activities to any important degree. With chloride ion at
25 millimoles/liter, Pd.sup.II activities were within 40-80% of those in
the absence of chloride ions, and still about 100 times greater than for a
typical Wacker catalyst system under comparable conditions.
Even more surprisingly discovered, as the hydrogen ion concentration is
decreased below 0.1 moles/liter, a region where Pd.sup.II activity in the
absence of chloride ions decreases substantially, Pd.sup.II activity in
the presence of an effective concentration of chloride ions can be
substantially maintained. Said another way, intrinsic Pd.sup.II activity
in the presence of chloride can exceed Pd.sup.II activity in the absence
of chloride. In tested embodiments with hydrogen ion concentrations about
0.01 mole/liter, Pd.sup.II activity in the presence of 25 millimoles/liter
chloride ion were about 5 times greater than those without chloride.
When chloride ions are added to solutions of acidic solutions of Pd.sup.II
in water, a series of aquated chloride complexes are formed as the
chloride ion concentration is increased. Where the acidity is such to
provide Pd.sup.II (H.sub.2 O).sub.4.sup.2+ as the hydrolytic form, the
series is as follows (in each of the following equilibria a chloride ion
is added and a water is lost, to the right as written):
Pd(H.sub.2 O).sub.4.sup.2+ .revreaction.PdCl(H.sub.2 O).sub.3.sup.+
.revreaction.PdCl.sub.2 (H.sub.2 O).sub.2 .revreaction.PdCl.sub.3 (H.sub.2
O).sup.- .revreaction.PdCl.sub.4.sup.= ( 18)
As the acidity of a solution is decreased, each of the complexes containing
coordinated water can dissociate a hydrogen ion to leave a complex of
coordinated hydroxide. With the successive replacement of coordinated
water in Pd(H.sub.2 O).sub.4.sup.2+ by chloride ions (equation (18)), the
positive charge on the palladium complex is decreased and the pK.sub.a for
deprotonation of remaining coordinated water is increased. This increase
in pK.sub.a by chloride coordination appears sufficient so that the
chloro-aquo species formed in the presence of moderate amounts of
chloride, are not significantly deprotonated to chloro-hydroxo species as
the hydrogen ion concentration is decreased to at least 0.01
millimoles/liter. Thereby, the Pd.sup.II catalyst activity of these
chloride-bound catalysts at hydrogen ion concentrations greater than 0.1
mole/liter can be substantially maintained on decreasing the hydrogen ion
concentration to at least 0.01 millimoles/liter. Further, the chloro-aquo
species appear substantially more active for olefin oxidation than
hydroxo-aquo species (such as Pd.sup.II (OH).sub.2 (H.sub.2 O).sub.2)
formed when Pd(H.sub.2 O).sub.4.sup.2+ is deprotonated as the hydrogen ion
concentration is decreased towards 0.01 millimoles/liter.
We have also discovered that in using the inventive chloride-comprising
catalyst solutions for the oxidation of olefins, chlorinated organic
by-products are not formed or are formed in amounts insignificant relative
to the amounts formed with the Wacker catalyst system. Apparently, the
essential absence of copper ions in preferred catalyst solutions which
include chloride, substantially avoids significant oxychlorination of
organics.
The polyoxoanion in the solutions and processes of the present invention
appears to provide two functions which are not provided with vanadium
alone in aqueous solution. First, the polyoxoanion solution provides an
environment for dissolution of suitably high concentrations of vanadium.
In acidic aqueous solutions with hydrogen ion concentrations comparable to
preferred solutions of the present invention, vanadium(V) alone exists
predominantly as the pervanadyl ion, VO.sub.2.sup.+ aq, whose solubility
is limited; at saturation, it deposits solid V.sub.2 O.sub.5. Likewise,
vanadium(IV) alone exists predominantly as the vanadyl ion, VO.sub.2.sup.+
aq, which saturates with respect to insoluble reduced vanadium oxides. In
contrast, polyoxoanions comprising vanadium can provide vanadium
solubilities to much higher concentrations, such as the decimolar to molar
level concentrations of vanadium utilized in preferred solutions and
processes of the present inventions.
Second, the polyoxoanion solution appears to enable suitably rapid reaction
of vanadium(IV) with oxygen, to regenerate vanadium(V) (reaction (13)).
Although pervanadyl ion is capable of palladium-catalyzed oxidation of
olefins, in a reaction similar to reaction (12), vanadyl ion alone reacts
only very slowly with dioxygen to regenerate pervanadyl. In contrast, in
our preferred polyoxoanion solutions, polyoxoanions comprising
vanadium(IV) react very rapidly with dioxygen, thereby providing preferred
processes of the present invention. Moreover, when vanadyl(IV) ion is
present in the polyoxoanion solution, it too can react rapidly with
dioxygen. Preferred polyoxoanions comprising vanadium, which enable
particularly rapid oxidation of vanadium(IV) to vanadium (V), further
comprise phosphorus or molybdenum. Particularly preferred polyoxoanions
further comprise both phosphorus and molybdenum.
Our processes, which include reaction of preferred polyoxoanion solutions
comprising vanadium(IV) with dioxygen, can proceed with volumetric
dioxygen reaction rates of at least 1 (millimole dioxygen/liter
solution)/second) and up to multiplicatively greater rates than those in
background references. Improved volumetric dioxygen reaction rates can be
achieved, in part, by operating the vanadium(IV)-dioxygen reaction process
under more efficient gas-liquid mixing conditions. It was surprisingly
discovered that these even improved rates are still limited by the
diffusion (mass transfer) of dioxygen into the aqueous solution, so that
still more rapid rates could be achieved under still more efficient
gas-liquid mixing conditions.
The air reactors in a Wacker-type acetaldehyde manufacturing plant provide
efficient gas-liquid mixing for achieving the commercially practicable
dioxygen reaction rates provided by the present invention. The dioxygen
reaction rates so achieved are suitable for utilization in manufacturing a
carbonyl product using a Wacker-type manufacturing plant.
We also surprisingly discovered that the presence of sulfate salts in
aqueous polyoxoanion solutions, such as those of background references
which are prepared by acidification using sulfuric acid, results in slower
volumetric dioxygen reaction rates. Rates of reaction which are limited by
diffusion (mass transfer) of a gas into a solution are a positive function
of the solubility of the gas in the solution. The presence of sulfate
salts may decrease ("salts-out") the solubility of dioxygen in aqueous
catalyst solutions and so decrease volumetric dioxygen reaction rates, but
there may be other explanations. In any case, in comparisons under the
same mixing and reaction conditions, polyoxoanion solutions comprising
vanadium(IV) react with dioxygen at greater volumetric reaction rates when
the solution is essentially free of sulfate ions.
Background references teach that volumetric reaction rates of reduced
polyoxoanion solutions with dioxygen decrease as the recited "pH"s of
solutions are decreased towards 1. Matveev patents specifically teach that
with "lower pH values" (their preferred "pH" is said to be 1), the rate of
the oxygen reaction is appreciably diminished. In contrast, we have found
that our solutions and processes oxidize vanadium(IV) in aqueous solution
by dioxygen at substantially undiminished volumetric dioxygen reaction
rates over a range of hydrogen ion concentrations extending substantially
greater than 0.1 mole/liter. Consequently, We are able to use high
hydrogen ion concentrations (e.g. greater than 0.1 mole/liter) to promote
palladium catalyst stability and olefin oxidation activity and yet
maintain exceptional polyoxoanion oxidant regeneration rates.
Catalyst Solution and Process Description
The following is additional description of the aqueous solutions of the
present invention and their use in processes for the oxidation of olefins
to carbonyl products:
Olefins
Olefins suitable for oxidation according to the process of this invention
are organic compounds having at least one carbon-carbon double bond, or
mixtures thereof. Examples of suitable olefins are compounds represented
by the formula RR'C.dbd.CHR" wherein R, R', and R" each represents a
hydrogen atom, a hydrocarbyl substituent, or a heteroatom selected from
the group halogen, oxygen, sulfur, or nitrogen, which may be the same or
different, and which may be connected in one or more ring structures.
Although there is no inherent limit on the size of the hydrocarbyl
substituents R, R', or R", they suitably may be linear, branched, or
cyclic as well as mononuclear or polynuclear aromatic. The hydrocarbyl
substituents described may be C.sub.1 to C.sub.20, although C.sub.1 to
C.sub.4 are especially preferred. Each hydrocarbyl substituent may also
contain one or more heteroatoms of halogen, oxygen, sulfur, or nitrogen.
The olefins themselves may be either cyclic or acyclic compounds. If the
olefin is acyclic, it can have either a linear structure or branched
structure, and the carbon-carbon double bond may be either terminal
("alpha-olefins") or non-terminal ("internal olefins"). If the olefin is
cyclic, the carbon-carbon double bond may have either one, both, or
neither of the carbon atoms of the double bond within the cycle. If the
olefin contains more than one carbon-carbon double bond, the double bonds
may be either conjugated or unconjugated.
Examples of suitable olefins are ethylene, propylene, 1-butene, 2-butene
(cis and trans), 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene,
1-octene, 1-decene, 1-dodecene, 1-hexadecene, 1-octadecene, 1-eicosene,
1-vinylcyclohexane, 3-methyl-1-butene, 2-methyl-2-butene,
3,3-dimethyl-1-butene, 4-methyl-1-pentene, 1,3-butadiene, 1,3-pentadiene,
1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, cyclopentene, cyclohexene,
cycloheptene, cyclooctene, cyclododecene, 1,5-cyclooctadiene,
1,5,9-cyclododecatriene. Preferred olefins are ethylene, propylene,
1-butene, cis-2-butene, trans-2-butene, 3-methyl-1-butene,
2-methyl-2-butene, 4-methyl-1-pentone, cyclopentene, and cyclohexene.
Mixtures of olefins may also be oxidized. Preferred mixtures of olefins
comprise olefins which yield a common carbonyl product on oxidation, for
example, mixtures of 1-butone, cis-2-butene, and/or trans-2-butene for the
production of 2-butanone, and mixtures of 3-methyl-1-butene and
2-methyl-2-butene for the production of 3-methyl-2-butanone.
The olefins introduced in the process of the present invention may be
diluted by other compounds which are inert towards the oxidation reaction
condition, for example, by dinitrogen, carbon dioxide, water and saturated
aliphatic compounds such as methane, ethane, propane, butane, cyclohexane,
and the like. For example, 1-butone, cis-2-butene, and/or trans-2-butene
for the oxidation process may be provided in admixture with butane;
cyclohexene may be provided in admixture with cyclohexane and/or benzene.
With gaseous olefins, the process involves mixing a gaseous olefinic phase
with the aqueous catalyst solution. With olefins which are liquid under
the reaction conditions, the process typically involves mixing an olefinic
liquid phase with the aqueous catalyst solution. Surfactants and/or
cosolvents may optionally be used to increase the solubility of the olefin
in the aqueous solution, or to increase the efficiency of diffusion (mass
transfer) of olefins into the aqueous catalyst solution, or both. See for
example, the surfactants and cosolvents disclosed in U.S. Pat. Nos.
4,434,082 and 4,507,507. Alternatively, cosolvents which miscibilize
otherwise separate olefinic and aqueous phases may be added. See for
example, the cyclic sulfone cosolvents disclosed in U.S. Pat. No.
4,507,506.
Dioxygen
Dioxygen may be introduced into processes of the present invention as
oxygen, air, or mixtures thereof (enriched air). The dioxygen may be in
admixture with an inert gas, for example, dinitrogen, carbon dioxide,
water vapor. The dioxygen is typically added to the process at a partial
pressure at least equal to its partial pressure in air at one atmosphere
pressure.
Carbonyl Products
The carbonyl products of the present invention are organic compounds
comprising at least one carbon-oxygen double bond: aldehydes, ketones,
carboxylic acids, and derivatives thereof. Acetaldehyde is the initial
catalytic reaction product of ethylene oxidation. Ketones are typically
the initial catalytic reaction products of oxidations of higher olefins.
For olefins which have double-bond positional isomers, mixtures of
isomeric ketones may be obtained. For example, 1-hexene may yield mixtures
of 2-hexanone and 3-hexanone.
The process of the present invention is highly selective to the initial
catalytic reaction products (acetaldehyde and ketones);they are formed
with selectivities typically higher than 80%, usually higher than 90%, and
often higher than 95%. These carbonyl products may be separated in high
yield from the reaction solution. Alternatively, the initial products may
be further oxidized by continued exposure to the oxidizing reaction
conditions, especially the dioxygen reaction for regenerating the oxidant.
Typically, the initial carbonyl products are oxidized to carboxylic acids
by such continued exposure. For example, acetaldehyde may be converted to
acetic acid, and cyclohexanone may be converted to adipic acid.
Palladium Catalysts
The palladium catalyst of the present invention may comprise any palladium
containing material which is suitable for oxidation of olefins under the
oxidation process conditions. The active palladium catalyst in the
solution may be provided to the solution as palladium(0), for example
palladium metal, or a palladium compound. Palladium(II) salts are
convenient sources of palladium catalyst. Preferred palladium(II) salts
include palladium acetate (Pd(CH.sub.3 CO.sub.2).sub.2), palladium
trifluoroacetate (Pd(CF.sub.3 CO.sub.2).sub.2), palladium nitrate
(Pd(NO.sub.3).sub.2), palladium sulfate (PdSO.sub.4), palladium chloride
(PdCl.sub.2), disodium tetrachloropalladate (Na.sub.2 PdCl.sub.4),
dilithium tetrachloropalladate (Li.sub.2 PdCl.sub.4), and dipotassium
tetrachloropalladate (K.sub.2 PdCl.sub.4).
It is preferred that palladium catalyst is dissolved in the aqueous
solution. When palladium(0) metal is the palladium source, it is dissolved
by oxidation to palladium(II) by the polyoxoanion oxidant. This oxidative
dissolution of palladium(0) to give active palladium catalyst generally
requires heating of the mixture, and is accelerated in the present
invention by the presence of chloride ions. Palladium(0) may be provided
as palladium metal or colloids. Palladium metal may be provided as bulk
metal (shot, wire, foil), palladium sponge, palladium black, palladium
powder, and the like.
Since palladium catalyst activity depends on such factors as the identity
of the olefin, olefin concentration dissolved in aqueous solution,
chloride ion concentration, hydrogen ion concentration, sulfate ion
concentration, temperature, and other reaction conditions, the palladium
concentration in the aqueous catalyst solution can vary in a broad range,
typically within 0.01 to 100 millimoles/liter. Although the preferred
palladium concentration will depend on other such aspects of the
embodiment, it can be readily determined for each application. The ratio
of the molar palladium concentration to the molar polyoxoanion
concentration will be an effective amount but less than 1. Preferred
palladium concentrations are generally 1/10 to 1/10000 of the
concentration of the polyoxoanion. For oxidation of gaseous olefins, such
as ethylene, propylene, and butenes, preferred palladium concentrations
are typically 0.1 to 10 millimolar. The present invention enables
practical ethylene oxidation reactions using palladium catalyst
concentrations less than 1.0 millimolar
Polyoxoanion and Polyoxoacid Oxidants
Polyoxoanions, and corresponding polyoxoacids, utilized as oxidants in the
present processes, are isopolyoxoanions and heteropolyoxoanions comprising
vanadium. A treatise on polyoxoanion compositions, structures, and
chemistry is found in Heteropoly and Isopoly Oxometailates by M. T. Pope,
Springer-Verlag, N.Y., 1983, which is incorporated by reference entirely.
Polyoxoanions comprising vanadium have at least one vanadium nucleus and
at least one other metal nucleus, which may be another vanadium nucleus or
any other metal nucleus which combines with vanadium in an oxoanion
composition.
Examples of suitable polyoxoanions and polyoxoacids are represented by the
general formula:
[H.sub.y X.sub.a M.sub.b M'.sub.c V.sub.x O.sub.z ].sup.m-
wherein:
H is proton bound to the polyoxoanion;
V is vanadium;
O is oxygen;
X is selected from the group consisting of boron, silicon, germanium,
phosphorus, arsenic, selenium, tellurium, and iodine--preferably
phosphorus;
M and M' are the same or different and are independently selected from the
group consisting of tungsten, molybdenum, niobium, tantalum, and
rhenium--preferably at least one of M and M' is molybdenum;
y, a, b, c, and m are individually zero or an integer (a is zero for
isopolyoxoanions and mixed isopolyoxoanions, or a is an integer for
heteropolyoxoanions);
x, and z are integers; and,
b+c+x is greater than or equal to 2.
Preferred polyoxoanions are the so-called Keggin heteropolyoxoanions
represented by the above general formula, additionally defined wherein:
a is one,
b+c+x is 12;
z is 40.
Most preferred are Keggin heteropolyoxoanions and heteropolyacids
comprising phosphorus, molybdenum, and vanadium (phosphomolybdovanadates),
represented by the following formula when in the oxidized state:
[H.sub.y PMo.sub.(12-x)V.sub.x O.sub.40 ].sup.(3+x-y)-
wherein:
x and y are integers;
0<x<12; and,
0.ltoreq.y.ltoreq.(3+x).
More specifically, 0.ltoreq.y.ltoreq.(3+x) for polyoxoanion species and
0.ltoreq.y.ltoreq.(3+x) for polyoxoacid species. Except when a polyoxo
species is completely deprotonated (i.e., y=0) or completely protonated
(i.e., y=(3+x)), it is both a polyoxoanion species and a polyoxoacid
species. However, protons dissociated into solution may also be considered
in designating a solution as comprising a polyoxoacid, even though all the
polyoxo species present may be fully deprotonated in the solution. The
Keggin phosphomolybdovanadates have been found to be anions of very strong
acids, and are believed never to be fully protonated in aqueous solution.
Preferred phosphomolybdovanadate solutions have phosphorus, molybdenum, and
vanadium present in relative molar amounts approximating the composition
of the Keggin heteropolyoxoanions; that is ([Mo]+[V]).congruent.12[P].
However, solutions having an excess of one or two components over these
ratios are also intended. In particular, excess phosphoric acid or
phosphate salt may be present. It is also intended that the Keggin
phosphomolybdovanadate solutions may optionally comprise excess vanadium
(for example, as VO.sub.2.sup.+) over the Keggin ratios.
The net negative charge of the polyoxoanions is balanced by countercations
which are protons and/or salt cations. When only protons are present as
countercations (when y=(3+x) for the Keggin phosphomolybdovanadic acid),
one has a "free acid" polyoxoacid. When one or more salt cations are
present as countercations, in place of protons, one has a polyoxoanion
salt, also called a salt of the polyoxoacid. When both protons and salt
cations are present, one has a partial salt of the polyoxoacid; the free
polyoxoacid is partially neutralized.
Suitable salt countercations are those which are inert, or in some way
advantageous (for example, Pd(H.sub.2 O).sub.4.sup.2+, VO.sub.2.sup.+),
under the reaction conditions. Preferred salt countercations are alkali
metal cations and alkaline earth cations which do not precipitate
insoluble polyoxoanion salts; for example: lithium, sodium, potassium,
beryllium, and magnesium cations, or mixtures thereof. Most preferred are
lithium (Li.sup.+), sodium (Na.sup.+), and magnesium (Mg.sup.2+) cations.
Mixtures of salt countercations may be present.
The Keggin phosphomolybdovanadates exist in aqueous solution as equilibrium
mixtures of anions varying in vanadium and molybdenum content (varying in
x). Moreover, for each value x such that 1<x<11, there are a number of
positional isomers for the placement of the vanadium and molybdenum in the
Keggin structure:for x=2 there are five isomers, for x=3 there are 13
isomers, for x=4 there are 27 isomers, and so on. Each of these
compositional and isomeric species has its own acid dissociation constants
which determine the extent to which it is protonated at a given hydrogen
ion concentration is solution. (That is, each compositional and isomeric
species can have its own average y value in a given solution.)
Accordingly, the compositions of aqueous Keggin phosphomolybdovanadate
solutions are not generally easily characterized in terms of a their
component species [H.sub.y PMo.sub.(12-x) V.sub.x O.sub.40 ].sup.(3+x-y)-
and their individual concentrations.
The present inventors have adopted a simplified, yet definitive, method of
designating the elemental constitution of solutions containing Keggin
phosphomolybdovanadate free acids or alkali metal salts in the oxidized
state, in terms of the general formula:
{A.sub.p H.sub.(3+n-p) PMo.sub.(12-n) V.sub.n O.sub.40 }
wherein:
A is an alkali metal cation (Li.sup.+, Na.sup.+);
the designated concentration of the solution is its phosphorus
concentration, usually reported in moles/liter (molar, M);
phosphorus, molybdenum, and vanadium are present in the concentration
ratios defined by n, and 0<n<12;
alkali metal is present in solution in a concentration ratio to phosphorus
defined by p, and 0.ltoreq.p.ltoreq.(3+n).
Accordingly, the negative charge of the designated Keggin formula in fully
deprotonated form, 3+n, is balanced in solution by p+q monocations. Since
this designation refers to a mixture of polyoxoanions, n and p may be
non-integral.
This designation completely defines the elemental constitution of an
aqueous solution. A given elemental constitution will have one
thermodynamic equilibrium distribution of species comprising its component
elements. When the phosphorus, molybdenum, and vanadium in these solutions
are predominantly present in Keggin heteropolyanions of formula [H.sub.y
PMo.sub.(12-x) V.sub.x O.sub.40 ].sup.(3+x-y)- (which is usually the case
in the preferred solutions of the present invention), then n is
approximately equal to the average value of x among the distribution of
species. The concentration of free hydrogen ions in such a solution is
approximately the concentration of phosphorus multiplied by the difference
between p and the average value of y among the distribution of species.
When the phosphomolybdovanadates are the only acids in solution, the
acidity of the solution can be set by the phosphomolybdovanadate
concentration, its identity (n), and the ratio of alkali cations (p) to
hydrogen ions (3+n-p).
Preferred phosphomolybdovanadate solutions following this method of
designation have 0<n<12. Especially preferred solutions have 2<n<6.
The concentration of the polyoxoanion can be varied over a broad range,
typically within 0.001 to 1.0 moles/liter. Preferred concentrations depend
strongly on the composition of the polyoxoanion, the specific application,
and the reaction conditions. For oxidation of gaseous olefins, such as
ethylene, propylene, and butenes, preferred polyoxoanion concentrations
are typically 0.1 to 1.0 molar.
The polyoxoanions can be provided to the aqueous catalyst solution by
dissolving prepared polyoxoanion solids (free acids or salts) or by
synthesis of the polyoxoanion directly in the aqueous solution from
component elemental precursors. Suitable polyoxoanion solids and
polyoxoanion solutions can be prepared by methods in the art, such as in
the background references cited in the section Background of the
Invention. For those solutions and related processes of the present
invention which are not required to be essentially free of sulfate ions,
the polyoxoanion may be prepared by the methods which add sulfuric acid in
the aqueous solution. U.S. Pat. No. 4,146,574, incorporated by reference
entirely, teaches a method for the preparation of solutions consisting of
free phosphomolybdovanadic acids.
Alternatively, the present invention provides a process for the direct
preparation of acidic aqueous solutions of salts of polyoxoacids
comprising vanadium without the introduction of mineral acids other than
the polyoxoacid or its component oxoacids. The acidity of the resulting
solutions is readily adjusted by the balance of salt cations and protons
in the salt.
Process for the Preparation of Polyoxoanion Solutions
According to the present invention, acidic aqueous solutions of salts of
polyoxoanions comprising vanadium are prepared by dissolving in water
oxides, oxoacids, and/or salts of oxoanions of the component polyoxoanion
elements, and optionally salts of carbonate, bicarbonate, hydroxide, and
oxide, such that the resulting ratio of protons and salt countercations
balancing the net negative charge of the resulting polyoxoanions in the
solution provides a hydrogen ion concentration in solution greater than
10.sup.-5 moles/liter.
Preferably, the resulting hydrogen ion concentration is greater than
10.sup.-3 moles/liter, and most preferably, greater than 0.1 moles/liter.
Preferred Keggin phosphomolybdovanadate salts are preferably prepared in
solution by dissolving vanadium oxide and/or vanadate salt, molybdenum
oxide and/or molybdate salt, phosphoric acid and/or phosphate salt, and
optionally carbonate, bicarbonate, and/or hydroxide salt in water, such
that the ratio of protons (3+n-p) and other salt countercations (p)
balancing the negative charge of the phosphomolybdovanadates (3+n)in the
solution provides the desired hydrogen ion concentration in the solution.
Preferably the vanadium, molybdenum, and phosphorus reactants are added in
ratios corresponding to the desired average Keggin composition of the
solution.
The temperature of the preparation process may be within the range
50.degree. to 120.degree. C. It is most conveniently operated in boiling
water at about 100.degree. C.
Typically, a solution of alkali vanadate, for example sodium metavanadate
(NaVO.sub.3) or hexasodium decavanadate (Na.sub.6 V.sub.10 O.sub.28), is
prepared in water. This solution can be prepared by dissolving solid salts
into water, but is prepared most economically by adding alkali carbonate
(e.g. Na.sub.2 CO.sub.3), alkali bicarbonate (e.g. NaHCO.sub.3), or alkali
hydroxide (e.g. NaOH) to a suspension of vanadium oxide (V.sub.2 O.sub.5)
in water and heating to complete the reactive dissolution. Then,
molybdenum oxide and phosphoric acid (or alkali phosphate salt) are added
to the alkali vanadate solution and heating is continued to complete the
preparation of an acidic aqueous phosphomolybdovanadate salt solution.
Finally, the solution is adjusted to the desired concentration by
evaporation and/or volumetric dilution.
Additional basic alkali salt (carbonate, bicarbonate, of hydroxide) can be
added at any point during or after the preparation to further neutralize
the resulting polyoxoacid solution and obtain decreased acidity; that is,
to adjust the value p in the designation {A.sub.p H.sub.(3+n-p)
PMo.sub.(12-n) VnO.sub.40 }.
When solutions having the same phosphorus concentration and vanadium
content, n, but different acidities (different p) are already prepared and
available, solutions of intermediate acidity (intermediate p) can be
prepared by blending the available solutions in the appropriate volumetric
ratios. More generally, solutions of determinate composition can be
prepared by blending measured volumes of two or more solutions, of known
phosphorus concentration, vanadium content (n), and salt cation content
(p).
Hydrogen Ions
Hydrogen ions and hydrogen ion concentrations, as used herein, have their
usual meaning. Hydrogen ions in aqueous solution are free, aquated
protons. Hydrogen ion concentration is not meant to include protons bound
in other solute species, such as in partially protonated polyoxoanions or
bisulfate.
Hydrogen ions may be provided by providing an acid which dissociates
protons when dissolved in aqueous solution. Organic and mineral acids
which are sufficiently acidic to provide the desired hydrogen ion
concentration are suitable. The acid is preferably inert to oxidation and
oxidative destruction under intended process conditions. Acid anhydrides
and other materials which hydrolytically release protons on reaction with
water may likewise be used to provide hydrogen ions.
Strong mineral acids, such as polyoxoacids, sulfuric acid, hydrochloric
acid, and the like, are preferred sources of hydrogen ions. Particularly
preferred are polyoxoacids. Certain solutions and related processes of the
present invention are essentially free of sulfuric acid. Certain solutions
and related processes of the present invention are essentially free of
mineral acids other than of polyoxoacids and hydrohalic acids.
Hydrogen ion concentrations of polyoxoanion solutions, as recited herein,
refer to the hydrogen ion concentration when essentially all the
polyoxoanion is in its fully oxidized state, which is when essentially all
the vanadium in the polyoxoanion solution is in the vanadium(V) state. It
has been determined that the acidity of the preferred polyoxoanion
solutions change with reduction, and these changes are not yet completely
understood and predictable. (For example, 0.30M {Na.sub.3 H.sub.3
PMo.sub.9 V.sub.3 O.sub.40 } solution has a hydrogen ion concentration
greater than 0.10 moles/liter in equilibrated fully oxidized state, but
less than 0.01 moles/liter in equilibrated fully reduced state, when all
the vanadium is in the vanadium(V) state.) The preferred polyoxoanions of
the present invention are most readily prepared essentially fully
oxidized, and can be readily returned to that condition by reaction with
dioxygen according to processes of the present invention. In the context
of determining hydrogen ion concentrations, the phrase "when essentially
all the oxidant is in its oxidized state" means when the solution of
oxidant is sufficiently oxidized so as to have the hydrogen ion
concentration which is obtained when it is fully oxidized.
The hydrogen ion concentration is sufficient to provide an acidic solution
having a hydrogen ion concentration greater than 10.sup.-5 mole/liter.
Preferably, the hydrogen ion concentration is greater than 10.sup.-3
moles/liter, and most preferably, greater than 0.1 moles/liter. Certain
solutions and related processes of the present invention specifically
comprise hydrogen ions at a concentration greater than 0.1 mole per liter
of solution when essentially all the oxidant is in its oxidized state.
Hydrogen Ion Concentration Measurement
Background references for polyoxoanion solutions generally recite "pH"
values for the solution but do not specify methods for determining them.
pH is technically defined as -log[a.sub.H +], where a.sub.H + is the
hydrogen ion activity. The hydrogen ion activity is identical to the
hydrogen ion concentration in otherwise pure water. The hydrogen ion
activity and hydrogen ion concentration are still good approximations of
each other in aqueous solutions which are low in ionic strength and
otherwise approximately ideal. Solutions of polyoxoacids at decimolar
concentrations, typical in background references and in the present
invention, have high ionic strength and are very non-ideal solutions,
especially when they also contain high concentrations of other mineral
acid salts.
The common method to obtain pH measurements of aqueous solutions uses
pH-sensitive glass electrodes, monitored with an electrometer (a "pH
meter"). Such electrodes are known to exhibit an "acid error", measuring
increasingly incorrect "pH"s as pH is decreased below 2 and especially at
real pH 1 and below. Moreover, successful measurement at any pH level
requires calibration with solutions of similar ionic media and ionic
strength. Common calibration solutions for pH meters are at relatively low
ionic strength and of very different ionic media compared to decimolar
polyoxoanion salt solutions. We have found that using different common
calibration solutions can lead to different "pH" measurements for the same
polyoxoanion solution. Unless a disclosure contains a recitation of the
method of "pH" measurement for these solutions, including the methods of
calibration, one having ordinary skill does not know what a reported "pH"
value really means, nor how to reproduce it.
We have developed a more definitive method of measuring hydrogen ion
concentration in the polyoxoanion solutions of the present invention. It
is based on the observation (by .sup.31 P- and .sup.51 V-NMR studies) that
in solutions designated {A.sub.p H.sub.(4-p) PMo.sub.11 VO.sub.40 },
PMo.sub.11 VO.sub.40.sup.4- is essentially the only species present. It
was further determined that PMo.sub.11 VO.sub.40.sup.4- remains completely
unprotonated even in concentrated solutions (>0.3M) of the free acid
{H.sub.4 PMo.sub.11 VO.sub.40 }. (Species having two or more vanadia do
become protonated in acidic aqueous solutions.) Accordingly, for solutions
of {A.sub.p H.sub.(4-p) PMo.sub.11 VO.sub.40 }, the hydrogen ion
concentration is the phosphorus concentration multiplied by (4-p). Such
solutions were prepared and used to calibrate glass pH electrodes for
measurement of the hydrogen ion concentration of solutions of undetermined
acidity, having the same phosphorus concentration. This method is
illustrated in the examples.
Sulfate Ions
Sulfate ions, as used herein, is meant to include both sulfate dianion
(SO.sub.4.sup.=) and bisulfate anion (HSO.sub.4.sup.-). Since sulfuric
acid is a very strong acid, addition of sulfuric acid to an aqueous
solution results in a solution of sulfate and/or bisulfate ions, depending
on the acidity of the solution.
Certain solutions and related processes of the present invention are
"essentially free of sulfate ions". This means the concentration of
sulfate and/or bisulfate salts is sufficiently low so that their undesired
influence on palladium catalyst activity, palladium catalyst stability,
volumetric olefin oxidation rate, or volumetric dioxygen reaction rate is
not significantly manifested. This can be readily determined
experimentally. Preferably, these solutions are free of sulfate and/or
bisulfate salts.
Chloride Ions
Chloride ions can be provided by any chloride-containing compound which
readily dissolves in water, or reacts with water, to release free, aquated
chloride ions into solution. Suitable chloride-containing compounds
include hydrochloric acid, chlorides and oxychlorides of oxoanion-forming
elements, chloride complexes and chloride salts, and the like. Examples of
chlorides and oxychlorides of the oxoanion-forming elements are PCl.sub.5,
POCl.sub.3, VOCl.sub.3, VOCl.sub.2, MoOCl.sub.4, and the like. Suitable
chloride salt countercations are those which are inert, or in some way
advantageous (for example, Pd.sup.II), under the reaction conditions and
which do not precipitate insoluble polyoxoanion salts out of aqueous
solution. Preferred chloride-containing compounds are hydrochloric acid,
palladium chloride compounds, and chloride salts of alkali metal cations
and alkaline earth cations which do not precipitate insoluble polyoxoanion
salts. Examples of suitable palladium chloride compounds are PdCl.sub.2,
Na.sub.2 PdCl.sub.4, K.sub.2 PdCl.sub.4, and the like. Examples of
suitable alkali and alkaline earth salts are lithium chloride (LiCl),
sodium chloride (NaCl), potassium chloride (KCl), and magnesium chloride
(MgCl.sub.2).
Significant amounts of chloride may also be present as impurities in the
starting materials for polyoxoanion preparation. For example, we
surprisingly discovered that several commercial sources of sodium vanadate
are sufficiently contaminated with chloride to provide effective amounts
of chloride in polyoxoanion solutions prepared from them.
Certain solutions and related processes of the present invention comprise
chloride at concentrations greater than coincidental to using PdCl.sub.2
as the palladium source; that is greater than twice the palladium
concentration. Preferably, the chloride concentration is greater than four
times the palladium concentration. Most preferably, the chloride
concentration is at least 5 millimolar. There is no particular upper limit
on the chloride concentration, but is preferably less than a concentration
at which the palladium catalyst activity becomes inversely dependent on
the square of the chloride concentration. Chloride is usually present at a
concentration of 0.001 to 1.0 moles/liter, preferably 0.005 to 0.50 moles
per liter, and most preferably 0.010 to 0.100 moles per liter. Typically,
the chloride is present in millimolar to centimolar concentrations, where
unquantified "millimolar concentrations" refers to concentrations of 1.0
to 10.0 millimolar, and unquantified "centimolar concentrations" refers to
concentrations of 10.0 to 100.0 millimolar. Generally, the chloride is
present in these solutions at a molar ratio of 10/1 to 10,000/1 relative
to palladium.
Chloride may also be provided by copper chlorides, for example by residual
Wacker catalyst retained in an industrial plant designed to operate the
Wacker process chemistry after draining the Wacker catalyst solution.
However, the chloride-containing solutions and related processes of the
present invention are preferably essentially free of copper ions.
"Essentially free of copper ions" means the olefin oxidation process with
the solution does not produce substantially higher amounts of chlorinated
organic by-products than a corresponding solution which is free of copper
ions.
Process Conditions
Broadly, olefin oxidation processes of the present reaction are conducted
under oxidative conditions sufficient to oxidize the olefin to a carbonyl
product. Likewise, in processes involving reaction of dioxygen, the
dioxygen reaction is conducted under oxidative conditions sufficient to
utilize dioxygen to oxidize the olefin, or intermediately, to regenerate
the polyoxoanion oxidant in its oxidized state.
The preferred temperature range for processes of the present invention
varies with the identity of the olefin and is interdependent with such
factors as the olefin concentration in aqueous solution, chloride ion
concentration, palladium concentration, and other factors which determine
reaction rates. Increasing temperature generally provides increased
reaction rates, although these increases are slight for reactions which
are limited by diffusion. In some cases, lower temperatures may be
preferred to avoid troublesome side-reactions. In two-stage operation,
temperatures for the olefin reaction and the dioxygen reaction can be set
independently. Generally, temperatures utilized in processes of the
present invention may range from about 20.degree. to about 200.degree. C.,
usually in the range 60.degree. to 160.degree. C. For gaseous olefins,
such as ethylene, propylene, and butenes, the temperature is preferably in
the range 90.degree. to 130.degree. C.
Pressures for the processes of the present invention depend strongly on the
nature of the olefin, whether gaseous or liquid under the reaction
conditions, whether dioxygen reaction is conducted simultaneously or
separately with the olefin oxidation reaction, whether oxygen is added as
oxygen or air, and reaction temperatures. For example, at reaction
temperatures less than 100.degree. C., the atmospheric boiling point of
water, with olefins which are liquid under the reaction conditions, in the
absence of dioxygen, the olefin oxidation process may be conveniently
conducted at atmospheric pressure. For temperatures near or above
100.degree. C. and above, water vapor contributes significantly to the
total pressure in the reactor device.
For gaseous olefins, elevated partial pressure is usually utilized to
increase the concentration of olefin in the gas phase in contact with the
liquid phase, and thereby increase its solubility in the liquid phase, to
increase reaction rates and decrease reactor volumes. Generally, gaseous
olefins are reacted at partial pressures of 1 atmosphere to 100
atmospheres, typically in the range 4 atmospheres (about 60 psi) to 20
atmospheres (about 300 psi). In two-stage mode, gaseous olefins are
preferably reacted at partial pressures in the range of 8 atmospheres
(about 120 psi) to 12 atmospheres (about 180 psi).
In certain solutions and processes of the present invention, olefin is
dissolved in the catalyst solution at concentrations effective for its
rate of oxidation to be at least 1 (millimole olefin/liter
solution)/second, or at concentrations effective to provide a palladium
turnover frequency of at least 1 (mole olefin/mole palladium)/second, or
preferably both. Reaction conditions and mixing conditions which meet
these criteria can be established by routine experimentation, for example
using the procedures of the following Examples. In certain solutions and
processes of the present invention, the olefin is dissolved at
concentrations such that its rate of oxidation is not further increased by
further increasing its concentration (olefin saturation kinetics).
For dioxygen reaction processes, elevated partial pressure is usually
utilized to increase the concentration of oxygen in the gas phase in
contact with the liquid phase, to increase reaction rates and decrease
reactor volumes. Generally, oxygen is reacted at partial pressures of 0.2
atmosphere (1 atmosphere air) to 100 atmospheres, typically in the range
0.2 atmospheres to 20 atmospheres, and preferably in the range 1
atmosphere (about 15 psi) to 10 atmosphere (about 150 psi).
For oxidation of gaseous olefins by dioxygen in two stage mode, the total
pressures in the olefin reactor and the dioxygen reactor are typically
similar, but may be varied independently. In two stage mode, compressed
air is typically used, but oxygen could be used as well.
For oxidation of gaseous olefins by dioxygen in one-stage mode, oxygen is
typically used and olefin and oxygen are typically fed in near
stoichiometric ratios, about 2:1.
Liquid olefins can be reacted neat or in combination with substantially
inert diluents. Generally, the concentration of the liquid olefin in a
second liquid olefinic phase is increased to increase reaction rates and
decrease reactor volumes. However, in some applications, it may be
advantageous to use a diluent. Such diluent may improve the mixing and
mass transfer of the olefin into the aqueous catalyst solution, or provide
improved recovery of the carbonyl product by improved liquid-liquid phase
distribution, and/or improved phase separation. In other applications, the
olefinic feed may be obtained in combination with substantially inert
diluents which are more easily or economically separated from the carbonyl
product than from the olefin. For example, butenes may be obtained in
combination with butane, cyclohexene may be obtained in combination with
cyclohexane and/or benzene. In other applications, it may be desirable to
use a cosolvent diluent which miscibilizes the olefinic and aqueous
solution components.
Suitable reactors for the processes of the invention provide for efficient
mixing of olefinic and aqueous catalyst phases. Efficient mixing in the
olefin reaction is established when the rate of the reaction is governed
by the chemical kinetics of catalysis, and is not limited by diffusion of
the olefin into the aqueous phase. Once that condition is established,
dissolved olefin concentration in the aqueous solution can be increased by
increasing the olefin concentration in the olefinic phase (for gaseous
olefins, by increasing the partial pressure of the olefin). In some
embodiments, the olefin concentration in the aqueous solution is effective
for the olefin oxidation rate to become independent of the olefin
concentration in the aqueous solution (olefin saturation kinetics).
Efficient mixing in the dioxygen reaction is established when the
diffusion-limited dioxygen reaction rate proceeds rapidly enough for
convenient and economical utilization in the intended application,
preferably at least 1 (millimole dioxygen/liter solution )/second.
Reactors and associated equipment in contact with the aqueous catalyst
solution should withstand the oxidizing nature of the solution and
processes without corrosion. For solutions and processes in the absence of
chloride, stainless steel, Hastelloy C, glass, and titanium provide
suitable equipment surfaces. For solutions and processes in the presence
of chloride, titanium and/or glass is preferred.
The carbonyl product of the reaction may be separated from the reaction
solution by usual methods such as vaporizing ("flashing" by pressure
drop), stripping, distilling, phase separation, extraction, and the like.
It is preferred that the carbonyl product is recovered while leaving the
aqueous solution in a form suitable to use directly in continued process
operation. In two-stage operation, it is preferred to remove the product
before the dioxygen reaction. In one-stage operation for a volatile
carbonyl product, it is preferred to continuously remove the product as it
is formed in the process.
Processes for the oxidation of palladium(0) to palladium(II) require only
that the palladium(0) is contacted with the polyoxoanion oxidant solution
under conditions sufficient to oxidize palladium(0) to palladium(II) at
the desired rate. Temperature, chloride ion concentration, and
palladium(0) surface area are particularly interdependent in determining
such conditions. Generally, the greater the chloride ion concentrations,
the lower the temperature required to achieve a desired rate. If the
dissolved palladium(II) is to be used in an olefin oxidation process, the
conditions are generally similar to those of the olefin oxidation process.
Solutions and Processes Wherein the Hydrogen Ion Concentration is Greater
Than 0.1 Mole/Liter
Solutions and related processes of the present invention wherein the
hydrogen ion concentration is greater than 0.1 mole/liter need not be
essentially free of sulfate, nor further comprise chloride ions, nor
further comprise any minimum dissolved olefin concentration. However,
preferred embodiments of such solutions and processes may include one or
more of these features.
Solutions and Processes Essentially Free of Sulfate
Solutions and related processes of the present invention which are
essentially free of sulfate ions need not also comprise a hydrogen ion
concentration greater than 0.1 mole/liter, nor further comprise chloride
ions, nor further comprise any minimum dissolved olefin concentration.
However, preferred embodiments of such solutions and processes may include
one or more of these features. In particular, it is preferred that the
hydrogen ion concentration of the solution be at least greater than
10.sup.-3 moles/liter.
Solutions and Processes Comprising Chloride
Solutions and related processes of the present invention using those
solutions which comprise chloride ions need not also comprise a hydrogen
ion concentration greater than 0.1 mole/liter, nor also be essentially
free of sulfate, nor further comprise any minimum dissolved olefin
concentration. However, preferred embodiments of such solutions and
processes may use one or more of these features. In particular, it is
preferred that the hydrogen ion concentration of the solution be at least
greater than 10.sup.-3 moles/liter.
It is especially preferred that solutions and processes which do not
provide effective concentrations of dissolved olefin, do comprise chloride
ions.
Solutions and Processes Comprising Dissolved Olefin at Effective
Concentrations
Solutions and related processes of the present invention which comprise
certain effective dissolved olefin concentrations in the aqueous catalyst
solution, and processes which comprise certain effective mixing conditions
need not also comprise a hydrogen ion concentration greater than 0.1
mole/liter, nor be essentially free of sulfate, nor further comprise
chloride ions. However, preferred embodiments of such solutions and
processes include one or more of these features. In particular, it is
preferred that the hydrogen ion concentration of the solution be at least
greater than 10.sup.-3 moles/liter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a scatter plot of measured palladium catalyst turnover
frequencies vs. -log[H.sup.+ ] (the negative base 10 logarithm of the
hydrogen ion concentration in moles per liter)in solutions of 0.30M
{Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 } reacted at 120.degree.
C. with ethylene at 150 psi partial pressure. The number next to each data
point is the number of the corresponding Example which follows.
FIG. 2 is a scatter plot of ethylene reaction rates vs. palladium catalyst
concentrations measured using 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40
} reacted at 115.degree. C. with ethylene at 150 psi partial pressure. The
data points correspond to Examples 32-35 (Table 2) which follow.
FIG. 3 is a scatter plot of dioxygen reaction rates vs. impeller stirring
rates measured for vanadium(IV)-polyoxoanion solutions in each of three
stirred tank autoclave reactor configurations under different reaction
conditions. Within each data series, the vanadium(IV)-polyoxoanion
solution, the partial pressure of dioxygen, and the reaction temperature
were the same. The three data series correspond to Examples 58 (Table 6),
59 (Table 7), and 60 (Table 8) which follow.
EXAMPLES
Without further elaboration, it is believed that one skilled in the art
can, using the preceding description, utilize the present invention to its
fullest extent. The following specific examples are, therefore, intended
to be merely illustrative, and not limitative of the disclosure in any way
whatsoever. Further exemplification is provided in patent application Ser.
Nos. 07/934,643, and 07/675,937, now abandoned, each of which is
incorporated by reference entirely.
Every -log[H.sup.+ ] value recited in these examples and in the drawings is
the base 10 logarithm of the hydrogen ion concentration in units of
mole/liter. Thus, -log[H.sup.+ ]=1.0 corresponds to a hydrogen ion
concentration of 0.10 mole/liter, and a -log[H.sup.+ ]<1.0 corresponds to
a hydrogen ion concentration greater than 0.10 mole/liter
Preparations of Polyoxoanion Solutions
Examples 1 through 8 and 10 through 31 show preparations of solutions of
polyoxoanions within the scope of the invention which are useful in the
inventive catalyst solutions and processes. Except when otherwise stated,
the exemplified polyoxoanion syntheses from H.sub.3 PO.sub.4, MoO.sub.3,
and V.sub.2 O.sub.5 were conducted in a 3 neck Morton flask, of 5.0 liter
or 12.0 liter capacity, equipped with an electric heating mantle, an
efficient reflux condenser/demister, a powder addition funnel and a high
torque overhead mechanical stirrer. Distilled water rinses were used for
every solution transfer in the preparations to ensure essentially
quantitative recovery of dissolved solution components in the final
solution.
Examples 1 through 8 illustrate preparations of the Keggin polyoxoanion
PMo.sub.11 VO.sub.40.sup.4- in solutions designated {A.sub.p H.sub.(4-p)
PMo.sub.11 VO.sub.40 }, which are particularly useful as calibration
standards for the determination of hydrogen ion concentrations in the
inventive catalyst solutions.
Example 1
Preparation of 0.30M {H.sub.4 PMo.sub.11 VO.sub.40 }
An aqueous solution of the phosphomolybdovanadic free acid H.sub.4
PMo.sub.11 VO.sub.40 was prepared according to the following reaction
equation:
0.5 V.sub.2 O.sub.5 +11 MoO.sub.3 +H.sub.3 PO.sub.4 +0.5 H.sub.2
O.fwdarw.H.sub.4 PMo.sub.11 VO.sub.40 (aq)
45.47 grams granular V.sub.2 O.sub.5 (0.25 mole) and 791.67 grams MoO.sub.3
(5.50 mole) were suspended in 5.0 liters distilled water with moderate
stirring. 57.37 grams 85.4% (w/w) H.sub.3 PO.sub.4 (0.50 mole) was added,
the mixture was diluted to a total volume of 10.0 liters with an
additional 4.5 liters of distilled water, and the mixture was heated to
reflux. After 2 days at reflux, 15 drops of 30% H.sub.2 O.sub.2 was added
dropwise to the mixture. The mixture was maintained at reflux for a total
of 7 days, giving a slightly turbid light burgundy-red mixture. The
mixture was cooled to room temperature and clarified by vacuum filtration.
The volume of the solution was reduced to about 1.5 liters by
rotating-film evaporation at 50.degree. C. under vacuum. The resulting
homogenous, clear, burgundy-red solution was volumetrically diluted with
distilled water to a total volume of 1.667 liters, giving 0.30 molar
H.sub.4 PMo.sub.11 VO.sub.40.
H.sub.4 PMo.sub.11 VO.sub.40 is a very strong acid whose four acidic
hydrogens are completely dissociated from the polyoxoanion as hydrogen
ions in this solution. The hydrogen ion concentration of this solution is
explicitly 1.2 mole/liter; -log[H.sup.+ ]=-0.08.
Example 2
Preparation of 0.30M {Na.sub.4 PMo.sub.11 VO.sub.40 }
An aqueous solution of the phosphomolybdovanadate full salt Na.sub.4
PMo.sub.11 VO.sub.40 was prepared according to the following reaction
equations:
0.5 V.sub.2 O.sub.5 +0.5 Na.sub.2 CO.sub.3 .fwdarw.NaVO.sub.3 (aq)+0.5
CO.sub.2 .Arrow-up bold.
1.5 Na.sub.2 CO.sub.3 +NaVO.sub.3 (aq)+11 MoO.sub.3 +H.sub.3 PO.sub.4
.fwdarw.Na.sub.4 PMo.sub.11 VO.sub.40 +1.5 CO.sub.2 .Arrow-up bold.+3/2
H.sub.2 O
109.13 grams granular V.sub.2 O.sub.5 (0.60 mole) was suspended in 1.0
liter distilled water in a Morton flask with overhead stirring. The
mixture was heated to ca. 60.degree. C. and 63.59 grams, granular Na.sub.2
CO.sub.3 (0.60 mole) was slowly added in portions to the rapidly stirred
suspension, causing CO.sub.2 liberation and dissolution of the V.sub.2
O.sub.5 to give an essentially homogeneous solution. The solution was
heated at reflux for 60 minutes. Approximately 1 ml of 30% H.sub.2 O.sub.2
was added dropwise to the mixture, which was maintained at reflux for an
additional 60 minutes, them cooled to room temperature. The solution was
clarified by vacuum filtration, and the resulting clear, orange sodium
vanadate solution was then returned to a Morton flask with additional
distilled water. 1900.01 grams MoO.sub.3 (13.2 mole) was added with rapid
stirring, the mixture was heated to about 60.degree. C., and 190.78 grams
granular Na.sub.2 CO.sub.3 (1.80 mole) was slowly added in portions to the
rapidly stirred suspension, causing CO.sub.2 liberation and dissolution of
MoO.sub.3. 137.70 grams 85.4% (w/w) H.sub.3 PO.sub.4 (1.20 mole) was then
slowly added to the mixture, and the mixture was heated at the reflux and
thereby converted to a clear, dark, burgundy-brown solution. After 3 hours
at reflux, the homogenous solution was cooled to room temperature and
volumetrically diluted with distilled water to a total volume of 4.0
liters, giving 0.30 molar {Na.sub.4 PMo.sub.11 VO.sub.40 }.
Example 3
Preparation of 0.30M {Li.sub.4 .sub.P Mo.sub.11 VO.sub.40 }
The procedure was the same as for {Na.sub.4 PMo.sub.11 VO.sub.40 } in
Example 2 except that 133.00 grams granular Li.sub.2 CO.sub.3 (1.80 mole)
was substituted for the Na.sub.2 CO.sub.3.
These solutions of 0.30M {A.sub.4 PMo.sub.11 VO.sub.40 }, A.dbd.Na, Li,
were found to be reproducibly slightly acidic, having hydrogen ion
concentrations .about.0.001M. Presumably, a minute fraction of the Keggin
polyoxoanion is hydrolytically dissociated, with release of hydrogen ions
from water, at equilibrium. 162 MHz .sup.31 P-NMR and 105 MHz .sup.51
V-NMR spectra of these solutions were essentially identical to those of
0.30M {H.sub.4 PMo.sub.11 VO.sub.40 }, showing substantially only the
PMo.sub.11 VO.sub.40.sup.4- ion.
Examples 4-8
Preparations of 0.30M {A.sub.p H.sub.(4-p) PMo.sub.11 VO.sub.40 },
A.dbd.Na, Li
The following 0.30M {A.sub.p H.sub.(4-p) PMo.sub.11 VO.sub.40 } solutions
were prepared by blending 0.30M {H.sub.4 PMo.sub.11 VO.sub.40 } (Example
1) and 0.30M {A.sub.4 PMo.sub.11 VO.sub.40 }, A.dbd.Na (Example 2) or Li
(Example 3) in (4-p):p volumetric ratios. The hydrogen ion concentration
in each of these solutions is explicitly 0.30(4-p) mole/liter, as
indicated:
______________________________________
Example 4:
0.30 M {Na.sub.0.67 H.sub.3.33 PMo.sub.11 VO.sub.40 }
-log[H.sup.+ ] = 0.00
Example 5:
0.30 M {Na.sub.3.67 H.sub.0.33 PMo.sub.11 VO.sub.40 }
-log[H.sup.+ ] = 1.00
Example 6:
0.30 M {Li.sub.0.67 H.sub.3.33 PMo.sub.11 VO.sub.40 }
-log[H.sup.+ ] = 0.00
Example 7:
0.30 M {Li.sub.3.67 H.sub.0.33 PMo.sub.11 VO.sub.40 }
-log[H.sup.+ ] = 1.00
Example 8:
0.30 M {Li.sub.2.67 H.sub.1.33 PMo.sub.11 VO.sub.40 }
-log[H.sup.+ ] = 0.40
______________________________________
Each of these solutions is alternatively prepared by adding the appropriate
amount of the alkali (Na, Li) carbonate, bicarbonate or hydroxide to the
{H.sub.4 PMo.sub.11 VO.sub.40 } solution or to a {A.sub.p H.sub.(4-p)
PMo.sub.11 VO.sub.40 } solution of lesser p.
The following Example shows a method for measurement of the hydrogen ion
concentration in acidic aqueous polyoxoanion solutions and corresponding
catalyst solutions, which is particularly preferred for determining
hydrogen ion concentrations in such solutions having hydrogen ion
concentrations greater than 0.10 mole/liter. The described procedures were
used to determine all of the hydrogen ion concentrations recited in the
present examples and in the drawings, usually expressed as -log[H.sup.+ ].
These recited hydrogen ion concentrations were measured with the indicated
polyoxoanions in solution in their oxidized state.
Example 9
Measurement of Hydrogen Ion Concentration
-log[H.sup.+ ] measurements were made with a commercial glass combination
pH electrode ((Orion) Ross Combination pH electrode) and commercial
digital-display pH potentiometer (Corning, Model 103, portable pH meter).
In pH display mode, the potentiometer was calibrated to display 1.00 with
the electrode in 0.30M {Na.sub.3.67 H.sub.0.33 PMo.sub.11 VO.sub.40 }
(Example 5) and 0.00 in 0.30M {Na.sub.0.67 H.sub.3.33 PMo.sub.11 VO.sub.40
} (Example 4), without intermediate adjustment. This calibration was used
to measure -log[H.sup.+ ] in 0.30M {Na.sub.p H.sub.(3+n-p) PMo.sub.(12-n)
V.sub.n O.sub.40 } solutions with p.gtoreq.0 having -log[H.sup.+
].ltoreq.1.00.
To measure -log[H.sup.+ ] in 0.30 M {Na.sub.p H.sub.(3+n-p) PMo.sub.(12-n)
V.sub.n O.sub.40 } solutions having -log[H.sup.+ ]>1.00, the potentiometer
was instead calibrated with the 0.30M {Na.sub.3.67 H.sub.0.33 PMo.sub.11
V.sub.1 O.sub.40 } solution, -log[H.sup.+ ]=1.00, and 0.10 M Na.sub.1.6
H.sub.1.4 PO.sub.4 pH 7.0 buffer (prepared from Na.sub.2 HPO.sub.4
.multidot.7H.sub.2 O and NaH.sub.2 PO.sub.4 .multidot.H.sub.2 O in
distilled water), taken to be -log[H.sup.+ ]=7.0. (pH 7 is far from the
hydrogen ion concentrations in the so measured polyoxoanion solutions, so
that any discrepancy between pH and -log[H.sup.+ ] in this calibration
solution only insignificantly effects the accuracy of those measurements.)
To measure -log[H.sup.+ ] in 0.30M {Li.sub.p H.sub.(3+n-p) PMo.sub.(12-n)
V.sub.n O.sub.40 } solutions with p>0, the corresponding Li.sup.+
calibration solutions were used: 0.30M {Li.sub.0.67 H.sub.3.33 PMo.sub.11
VO.sub.40 }, -log[H.sup.+ ]=0.00 (Example 6); 0.30M {Li.sub.3.67
H.sub.0.33 PMo.sub.11 VO.sub.40 }, -log[H.sup.+ ]=1.00 (Example 7); and
0.10M Li.sub.1.6 H.sub.1.4 PO.sub.4 (prepared from H.sub.3 PO.sub.4 and
LiOH in distilled water), taken to be -log[H.sup.+ ]=7. By this
calibration, 0.30M {Li.sub.2.67 H.sub.1.33 PMo.sub.11 VO.sub.40 } (Example
8), with known -log[H.sup.+ ]=0.40, was measured to be -log[H.sup.+
]=0.37, indicating the accuracy of the measurement.
To measure -log[H.sup.+ ] in solutions having other Keggin polyoxoanion
concentrations, calibration solutions of {A.sub.p H.sub.(4-p) PMo.sub.11
VO.sub.40 } at the same other polyoxoanion concentration are used:
-log[H.sup.+ ] for X M {A.sub.p H.sub.(4-p) PMo.sub.11 VO.sub.40 } is
X(4-p).
Although hydrogen ion concentrations were quantitatively measured for the
polyoxoanion and catalyst solutions in the present Examples, it is often
sufficient to simply discriminate qualitatively whether the hydrogen ion
concentration is greater than or less than 0.10 mole/liter. A single
calibration solution of {A.sub.p H.sub.(4-p) PMo.sub.11 VO.sub.40 } with a
hydrogen ion concentration of 0.10 mole/liter can be used to determine if
another polyoxoanion solution has a hydrogen ion concentration greater
than or less than 0.10 mole/liter by comparison. Preferably, the
calibration solution has the same polyoxoanion concentration and the same
salt countercation as the other solution in question. Any physical
measurement technique capable of discriminating between solutions having
hydrogen ion concentrations greater than or less such a single calibration
solution is suitable for making the comparison.
Example 10
Preparation of 0.317M {H.sub.4.9 PMo.sub.10.1 V.sub.1.9 O.sub.40 }
Preparation of a desired phosphomolybdic free acid solution 0.30M {H.sub.5
PMo.sub.10 V.sub.2 O.sub.40 } by the following reaction equation was
attempted by adapting the procedures exemplified in U.S. Pat. No.
4,156,574:
H.sub.3 PO.sub.4 +V.sub.2 O.sub.5 +10 MoO.sub.3 +H.sub.2 O.fwdarw.H.sub.5
PMo.sub.10 V.sub.2 O.sub.40 (aq)
545.64 grams granular V.sub.2 O.sub.5 (3.00 mole) and 4318.20 grams
MoO.sub.3 (30.00 mole) were suspended in 4.0 liters distilled water with
moderate stirring. 344.23 grams 85.4% (w/w) H.sub.3 PO.sub.4 (3.00 mole)
was added, the mixture was diluted to a total volume of 10.0 liters with
an additional 4.7 liters of distilled water, and the stirring mixture was
heated to reflux. The mixture was maintained at reflux for 7 days, after
which it was cooled to room temperature, the stirring was stopped, and the
undissolved solids were allowed to fall for five days. The burgundy-red
supernatant solution was decanted from yellow residue. Repeatedly, the
residue was suspended in water, the suspension was centrifuged, and the
supernatant was decanted. These wash supernatants were combined with the
original supernatant and the resulting solution was clarified by vacuum
filtration. The volume of the solution was reduced to about 9 liters by
rotating-film evaporation at 50.degree. C. under vacuum.
The yellow residue was dried over CaCl.sub.2 dessicant under vacuum. The
dry mass was 39.46 grams and was analyzed to be essentially completely
V.sub.2 O.sub.5 by quantitative elemental analyses for P, Mo, and V. The
vanadium content of the polyoxoacid solution was determined by difference.
Accordingly, the solution was volumetrically diluted with distilled water
to a total volume of 9.379 liters to provide a vanadium concentration of
0.600 gram-atoms per liter.
The composition of this solution is designated 0.317M {H.sub.4.9
PMo.sub.10.1 V.sub.1.9 O.sub.40 }+0.003M H.sub.3 PO.sub.4. Alternatively,
the solution may be viewed as 0.285M H.sub.5 PMo.sub.10 V.sub.2 O.sub.40
+0.032M H.sub.4 PMo.sub.11 VO.sub.40 +0.003M H.sub.3 PO.sub.4. Its
hydrogen ion concentration was measured to be 1.16 mole per liter;
-log[H.sup.+ ]=-0.07.
Example 11
Preparation of 0.30M {Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 }
An aqueous phosphomolybdovanadic acid partial salt solution designated
0.30M {Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 } was prepared
according to the following reaction equations:
V.sub.2 O.sub.5 +Na.sub.2 CO.sub.3 .fwdarw.2 NaVO.sub.3 (aq)+CO.sub.2
.Arrow-up bold.
2 NaVO.sub.3 (aq)+10 MoO.sub.3 +H.sub.3 PO.sub.4 .fwdarw.Na.sub.2 H.sub.3
PMo.sub.10 V.sub.2 O.sub.40 (aq)
218.26 grams granular V.sub.2 O.sub.5 (1.20 mole) was suspended in 2.0
liters distilled water in a Morton flask with overhead stirring and the
mixture was heated to about 60.degree. C. 127.19 grams granular Na.sub.2
CO.sub.3 (1.20 mole) was slowly added in portion to the rapidly stirred
mixture, causing CO.sub.2 liberation and dissolution of the V.sub.2
O.sub.5 to give an essentially homogeneous solution. The solution was
heated at the reflux for 60 minutes. The solution was then lime green
color due to dissolved V.sup.IV which was originally present in the
V.sub.2 O.sub.5. Approximately 1 ml of 30% H.sub.2 O.sub.2 was added
dropwise to the mixture causing the dark, black-blue green color to fade,
leaving a slightly turbid, pale-tan sodium vanadate solution. The solution
was maintained at reflux for an additional 60 minutes to ensure the
decomposition of excess peroxide and then cooled to room temperature. The
solution was clarified by vacuum filtration to remove the small amount
(<0.1 grams) of brown solid which contained almost all the iron and silica
impurities originally present in the V.sub.2 O.sub.5. The clear, orange
sodium vanadate solution was then returned to a Morton flask, and 1727.28
grams MoO.sub.3 (12.00 mole) was added with rapid overhead stirring. The
mixture was heated to about 60.degree. C. and 137.7 grams 85.4% (w/w)
H.sub.3 PO.sub.4 (1.20 mole) was added. The mixture was heated at the
reflux and thereby convened to a clear, dark, burgundy-red solution. After
3 hours at reflux, the homogenous burgundy-red solution was cooled to room
temperature and volumetrically diluted with distilled water to a total
volume of 4.00 liters, giving 0.30M {Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2
O.sub.40 }.
The hydrogen ion concentration of 0.30M {Na.sub.2 H.sub.3 PMo.sub.10
V.sub.2 O.sub.40 } was measured to be 0.67 mole/liter; -log[H.sup.+
]-0.18.
Example 12
Preparation of 0.30M {Na.sub.5 PMo.sub.10 V.sub.2 O.sub.40 }
An aqueous phosphomolybdovanadate full salt solution designated 0.30M
{Na.sub.5 PMo.sub.10 V.sub.2 O.sub.40 }]was prepared according to the
following reaction equations:
V.sub.2 O.sub.5 +Na.sub.2 CO.sub.3 .fwdarw.2 NaVO.sub.3 (aq)+CO.sub.2
.Arrow-up bold.
1.5 Na.sub.2 CO.sub.3 +2 NaVO.sub.3 (aq)+10 MoO.sub.3 +H.sub.3 PO.sub.4
.fwdarw.Na.sub.5 PMo.sub.10 V.sub.2 O.sub.40 +1.5 CO.sub.2 .Arrow-up
bold.+1.5 H.sub.2 O
The procedure was the same as in Example 11 except that after the addition
of the MoO.sub.3, the mixture was heated to the reflux and an additional
190.78 grams granular Na.sub.2 CO.sub.3 (1.80 mole) was slowly added in
portions to the stirred suspension, causing CO.sub.2 liberation, before
the addition of the H.sub.3 PO.sub.4.
Examples 13-17
Preparations of 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 }
Solutions
The following polyoxoacid partial salt solutions designated 0.30M {Na.sub.p
H.sub.(.sub.5-p) PMo.sub.10 V.sub.2 O.sub.40 } were prepared by blending
0.30M {Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 } (Example 11) and
0.30M {Na.sub.5 PMo.sub.10 V.sub.2 O.sub.40 } (Example 12) in (5-p):(p-2)
volumetric ratios, and their hydrogen ion concentrations were measured as
indicated:
______________________________________
Example 13
0.30 M {Na.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 }
-log[H.sup.+ ] = 0.69
Example 14
0.30 M {Na.sub.4.40 H.sub.0.60 PMo.sub.10 V.sub.2 O.sub.40
-log[H.sup.+ ] = 0.91
Example 15
0.30 M {Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40
-log[H.sup.+ ] = 1.00
Example 16
0.30 M {Na.sub.4.80 H.sub.0.20 PMo.sub.10 V.sub.2 O.sub.40
-log[H.sup.+ ] = 1.43
Example 17
0.30 M {Na.sub.4.94 H.sub.0.06 PMo.sub.10 V.sub.2 O.sub.40
-log[H.sup.+ ] = 1.96
______________________________________
Each of these solutions is alternatively prepared by direct synthesis (see
for example the preparation of 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2
O.sub.40 } in Example 22) or by adding the appropriate amount of the
sodium carbonate, bicarbonate or hydroxide to a 0.30M {Na.sub.p
H.sub.(5-p) PMo.sub.10V.sub.2 O.sub.40 } solution of lesser p.
Example 18
Preparation of 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 }
Solution With -log[H.sup.+ ]=1.00 Using Sulfuric Acid
An aqueous solution comprising 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10
V.sub.2 O.sub.40 } was prepared from Na.sub.3 PO.sub.4, MoO.sub.3, V.sub.2
O.sub.5, Na.sub.2 CO.sub.3, and H.sub.2 SO.sub.4 by the method of the
Matveev patents' Example 5 (designated H.sub.5 [PMo.sub.10 V.sub.2
O.sub.40 ] therein), with the following modifications: 1) a stoichiometric
amount of vanadium for the Keggin composition was added, not 5% excess; 2)
the solution was prepared to contain -log[H.sup.+ ]=1.00, measured
according to Example 9, instead the stated "pH 1.0" since the Matveev
patents give no indication how to calibrate or measure the stated "pH"
values or how much sulfuric acid to add to obtain them; and 3) the amount
of sulfuric acid added was measured with a buret in order to explicitly
know the complete composition of the resulting aqueous polyoxoanion
solutions; as follows.
27.28 grams granular V.sub.2 O.sub.5 (0.15 mole) and 215.91 grams MoO.sub.3
(1.50 mole) were suspended in 0.75 liter distilled water at about
60.degree. C. in a beaker. 37.02 grams Na.sub.3 PO.sub.4
.multidot.12H.sub.2 O (0.15 mole) was added to the rapidly stirring
mixture, followed by 23.85 grams granular Na.sub.2 CO.sub.3 (0.225 mole),
which was slowly added in portions, causing CO.sub.2 liberation. The
beaker was covered with a watchglass and the mixture was boiled for 90
minutes, resulting in a dark burgundy-red solution. The watch glass was
removed and the solution was boiled uncovered an additional 90 minutes to
reduce its volume to about 0.5 liter. The solution was then cooled to room
temperature, and its hydrogen ion concentration was measured to be
-log[H.sup.+ ]=5.2. 96% (w/w) H.sub.2 SO.sub.4 was added in portions to
the stirring solution to adjust its -log[H.sup.+ ] to 1.10, requiring 8.47
milliliters (0.153 mole). The solution was then boiled uncovered for 60
minutes, cooled to room temperature, and clarified by vacuum filtration to
remove a small amount of brown solid. It was then volumetrically diluted
with distilled water to a total volume of 0.500 liter. Its -log[H.sup.+ ]
was readjusted to 1.00 by adding 0.14 milliliter 96% (w/w) H.sub.2
SO.sub.4.
The total amount of sulfuric acid added into the solution was 0.155 mole.
Accordingly, the solution contained 0.31M sulfate anions (sulfate or
bisulfate), 0.30M polyoxoanion, and 1.80M sodium cations. Since the 0.30M
{Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40 } solution prepared
without sulfuric acid (Example 15) also measures -log[H.sup.+ ]=1.00, the
present solution was designated 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10
V.sub.2 O.sub.40 }+0.31M Na.sub.1.48 H.sub.0.52 SO.sub.4. This allocation
of sodium countercations is otherwise arbitrary, but this overall
designation defines the elemental composition of the solution. The Matveev
patents' designation as H.sub.5 [PMo.sub.10 V.sub.2 O.sub.40 ] does not
fully define the elemental composition, as it is silent on sodium and
sulfate content, and is grossly misleading, as the free polyoxoacid
solution 0.30M {H.sub.5 PMo.sub.10 V.sub.2 O.sub.40 } (Example 10)
measures -log[H.sup.+ ]<0.
Example 19
Preparation of 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 }
Solution With -log[H+]=0.18 Using Sulfuric Acid
An aqueous solution comprising 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10
V.sub.2 O.sub.40 } with a hydrogen ion concentration greater than 0.10
mole/liter (-log[H.sup.+ ]<0) was prepared by adding 2.0 milliliter 96%
(w/w) H.sub.2 SO.sub.4 (0.036 mole) to 100 milliliters of a solution
prepared by the method of Example 18 The solution then contained 0.67M
sulfate anions (sulfate or bisulfate), 0.30M polyoxoanion, and 1.80M
sodium cations, and measured -log[H.sup.+ ]=0.18. Since the 0.30M
{Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 } solution prepared without
sulfuric acid (Example 11) also measures -log[H.sup.+] =0.18, the present
solution was designated 0.30M {Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2
O.sub.40 }+0.67M Na.sub.1.8 H.sub.0.2 SO.sub.4. Again, this not a unique
allocation of sodium countercations, but the overall designation defines
the elemental composition of the solution.
Example 20
Preparation of 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40 }
Solution With Added Sodium Sulfate Salts and -log[H+]=1.00
To mimic the solution designated 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10
V.sub.2 O.sub.40 }+0.31M Na.sub.1.48 H.sub.0.52 SO.sub.4 prepared by the
method of the Matveev patents (Example 18), 2.13 grams Na.sub.2 SO.sub.4
(0.015 mole) and 2.21 grams NaHSO.sub.4 H.sub.2 O (0.016 mole) were
dissolved in 100 milliliters of 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10
V.sub.2 O.sub.40 } (Example 15). This solution measured -log[H.sup.+
]=0.85 instead of the expected 1.00. A second solution was prepared by
dissolving 4.40 grams Na.sub.2 SO.sub.4 (0.031 mole) to another 100
milliliters of 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40
}, and measured -log[H.sup.+ ]=1.28. Equal volumes of the two solutions
were blended to give a solution measuring -log[H.sup.+ ]=1.00 and
designated 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40
}+0.31M Na.sub.1.74 H.sub.0.26 SO.sub.4.
Example 21
Preparation of 0.30M {Li.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 }
The procedure was the same as for 0.30M {Na.sub.2 H.sub.3 PMo.sub.10
V.sub.2 O.sub.40 } in Example 11 except that granular Li.sub.2 CO.sub.3
was substituted for the Na.sub.2 CO.sub.3 and the preparation was scaled
to give 10.0 liter product solution.
545.64 grams granular V.sub.2 O.sub.5 (3.00 mole) was suspended in 2.0
liters distilled water in a Morton flask with overhead stirring and the
mixture was heated to about 60.degree. C. 221.67 grams granular Li.sub.2
CO.sub.3 (3.00 mole) was slowly added in portions to the rapidly stirred
mixture, causing CO.sub.2 liberation and dissolution of the V.sub.2
O.sub.5 to give and essentially homogeneous solution. The solution was
heated at the reflux for 60 minutes. The solution was then dark green due
to dissolved V.sup.IV which was originally present in the V.sub.2 O.sub.5.
Approximately 1 ml of 30% H.sub.2 O.sub.2 was added dropwise to the
mixture causing the dark, black-blue green color to fade, leaving a
slightly turbid, pale-tan sodium vanadate solution. The solution was
maintained at reflux for an additional 60 minutes to ensure the
decomposition of excess peroxide and then cooled to room temperature. The
solution was clarified by vacuum filtration to remove the small amount
(.about.0.1 grams) of brown solid which contained almost all the iron and
silica impurities originally present in the V.sub.2 O.sub.5. The clear,
orange sodium vanadate solution was then returned to a Morton flask, and
4318.20 grams MoO.sub.3 (30.00 mole) was added with rapid overhead
stirring. The mixture was heated to about 60.degree. C. and 344.24 grams
85.4% (w/w) H.sub.3 PO.sub.4 (3.00 mole) was added. The mixture was heated
at the reflux and thereby converted to a clear, dark, burgundy-red
solution. After 3 hours at reflux, the homogenous burgundy-red solution
was cooled to room temperature and volumetrically diluted with distilled
water to a total volume of 10.00 liters, giving 0.30M {Na.sub.2 H.sub.3
PMo.sub.10 V.sub.2 O.sub.40 }, having -log[H.sup.+ ]=0.10.
Example 22
Preparation of 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 }
An aqueous phosphomolybdovanadate partial salt solution designated 0.30M
{Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } was prepared according to the
following reaction equations:
V.sub.2 O.sub.5 +Li.sub.2 CO.sub.3 .fwdarw.2 LiVO.sub.3 (aq)+CO.sub.2
.Arrow-up bold.
1 Li.sub.2 CO.sub.3 +2 LiVO.sub.3 (aq)+10 MoO.sub.3 +H.sub.3 PO.sub.4
.fwdarw.Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 +1 CO.sub.2 .Arrow-up
bold.+1 H.sub.2 O
The procedure was the same as in Example 21 except that after the addition
of the MoO.sub.3, the mixture was heated to the reflux and an additional
221.67 grams granular Li.sub.2 CO.sub.3 (3.00 mole) was slowly added in
portions to the stirred suspension, causing CO.sub.2 liberation, before
the addition of the H.sub.3 PO.sub.4. The hydrogen ion concentration was
of 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } measured to be
-log[H.sup.+ ]=0.63
Example 23
Preparation of 0.30M {Li.sub.3.24 H.sub..sub.1.76 PMo.sub.10 V.sub.2
O.sub.40 }
This solution was prepared by blending 0.30M {Li.sub.2 H.sub.3 PMo.sub.10
V.sub.2 O.sub.40 }(Example 21) and 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2
O.sub.40 } (Example 22) in a (4-3.24):(3.24-2) volumetric ratio, and
measured -log[H+]=0.37.
Example 24
Preparation of 0.30M {Na.sub.3 PMo.sub.9 V.sub.3 O.sub.40 }
The phosphomolybdovanadic partial salt solution designated {Na.sub.3
H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 } was prepared according to the
following reaction equations:
1.5 V.sub.2 O.sub.5 +1.5 Na.sub.2 CO.sub.3 .fwdarw.3 NaVO.sub.3 (aq)+1.5
CO.sub.2 .Arrow-up bold.
3 NaVO.sub.3 (aq)+9 MoO.sub.3 +H.sub.3 PO.sub.4 .fwdarw.Na.sub.3 H.sub.3
PMo.sub.9 V.sub.3 O.sub.40 (aq)
818.46 grams granular V.sub.2 O.sub.5 (4.50 moles) was suspended in 3.5
liters distilled water in a Morton flask with overhead stirring and the
mixture was heated to about 60.degree. C. 476.95 grams granular Na.sub.2
CO.sub.3 (4.50 moles) was slowly added in portions to the rapidly stirred
mixture, causing CO.sub.2 liberation and dissolution of the V.sub.2
O.sub.5 to give and essentially homogeneous solution. The solution was
heated at the reflux for 60 minutes. The solution was then dark,
blue-green due to dissolved V.sup.IV which was originally present in the
V.sub.2 O.sub.5. Approximately 1 ml of 30% H.sub.2 O.sub.2 was added
dropwise to the mixture causing the dark, black-blue green color to fade,
leaving a slightly turbid, pale-tan sodium vanadate solution. The solution
was maintained at reflux for an additional 60 minutes to ensure the
decomposition of excess peroxide and then cooled to room temperature. The
solution was clarified by vacuum filtration to remove the small amount
(<0.2 grams) of brown solid which contained almost all the iron and silica
impurities originally present in the V.sub.2 O.sub.5. The clear, orange
sodium vanadate solution was then returned to a Morton flask, diluted with
4.0 liters distilled water, and 3886.38 grams MoO.sub.3 (27.00 moles) was
added with rapid overhead stirring. The mixture was heated to about
60.degree. C. and 344.25 grams 85.4% (w/w) H.sub.3 PO.sub.4 (3.00 moles)
was added. The mixture was heated at the reflux and thereby converted to a
clear, dark, burgundy-red solution. After 3 hours at reflux, the
homogenous solution was cooled to room temperature and volumetrically
diluted with distilled water to a total volume of 10.00 liters, giving
0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40}.
The hydrogen ion concentration of 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 } was measured to be 0.35 mole/liter; -log[H.sup.+ ]=0.45
Example 25
Preparation of 0.30M {Li.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 }
The procedure was the same as for 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 } in Example 24 except that 332.51 grams granular Li.sub.2
CO.sub.3 (4.50 moles) was substituted for the Na.sub.2 CO.sub.3. The
hydrogen ion concentration of the solution was measured as -log[H.sup.+
]=0.38
Example 26
Preparation of 0.30M {Li.sub.1.15 H.sub.5.85 PMo.sub.8 V.sub.4 O.sub.40 }
Preparation of an aqueous 0.30M {H.sub.7 PMo.sub.8 V.sub.4 O.sub.40 }
solution from stoichiometric quantities of H.sub.3 PO.sub.4, V.sub.2
O.sub.5, and MoO.sub.3 in water was attempted by adapting the method
described in U.S. Pat. No. 4,156,574, analogous to the preparation of
{H.sub.4.9 PMo.sub.10.1 V.sub.1.9 O.sub.40 } solution in Example 10.
However, Li.sub.2 CO.sub.3 was ultimately added to achieve complete the
incorporation of the V.sub.2 O.sub.5 into the polyoxoanion solution, as
described below. The overall equation for the synthesis became as follows:
H.sub.3 PO.sub.4 +2 V.sub.2 O.sub.5 +8 MoO.sub.3 +0.575 Li.sub.2 CO.sub.3
+1.425 H.sub.2 O.fwdarw.Li.sub.1.15 H.sub.5.85 PMo.sub.8 V.sub.4 O.sub.40
+0.575 CO.sub.2 .Arrow-up bold.
218.26 grams granular V.sub.2 O.sub.5 (1.20 mole) and 690.91 grams
MoO.sub.3 (4.80 mole) were suspended in 2.3 liters distilled water in a
Morton flask with moderate stirring. 68.85 grams 85.4% (w/w) H.sub.3
PO.sub.4 (0.60 mole) was added, the mixture was diluted to a total volume
of 6.0 liters with an additional 3.44 liters of distilled water, and the
stirring mixture was heated to reflux. The mixture was maintained at
reflux for 7 days, after which it was cooled to room temperature, the
stirring was stopped, and the undissolved solids were allowed to fall for
two days. The burgundy-red supernatant solution was decanted from a yellow
residue (composed principally of V.sub.2 O.sub.5). Repeatedly, the residue
was suspended in water, the suspension was centrifuged, and the
supernatant was decanted. These wash supernatants were combined with the
original and returned to the Morton flask.
The V.sub.2 O.sub.5 residue was transferred into another flask with about
0.5 liters distilled water and the mixture was heated to about 60.degree.
C. 25.49 grams Li.sub.2 CO.sub.3 chips (0.60 moles) was slowly added in
portions to the rapidly stirred mixture, causing CO.sub.2 liberation and
dissolution of the V.sub.2 O.sub.5. The resulting mixture was heated at
the reflux for 60 minutes, giving a brown-red, slightly turbid solution.
Approximately 1 ml of 30% H.sub.2 O.sub.2 was added dropwise to the
solution which was then refluxed for an additional 60 minutes to ensure
the decomposition of excess peroxide. The orange lithium vanadate solution
was cooled to room temperature, clarified by vacuum filtration, and added
to the original supernatant solution in the Morton flask.
The entire solution was heated to reflux for about 3 hours, then cooled to
room temperature. The volume of the solution was reduced to about 1.8
liters by rotating-film evaporation at 50.degree. C. under vacuum. The
homogeneous, dark burgundy-red solution was volumetrically diluted with
distilled water to a total volume of 2.0 liters, giving 0.30M {Li.sub.1.15
H.sub.5.85 PMo.sub.8 V.sub.4 O.sub.40 }, having -log[H.sup.+ ]=0.13.
Example 27
Preparation of 0.30M {Li.sub.4 H.sub.3 PMo.sub.8 V.sub.4 O.sub.40 }
The polyoxoacid partial salt solution 0.30M {Li.sub.4 H.sub.3 PMo.sub.8
V.sub.4 O.sub.40 } was prepared analogously to 0.30M {Li.sub.3 H.sub.3
PMo.sub.9 V.sub.3 O.sub.40 } (Example 25) and 0.30M {Li.sub.2 H.sub.3
PMo.sub.10V.sub.2 O.sub.40 } (Example 21), according to the following
reaction equations:
2 V.sub.2 O.sub.5 +2 Li.sub.2 CO.sub.3 .fwdarw.4 LiVO.sub.3 (aq)+2 CO.sub.2
.Arrow-up bold.
4 LiVO.sub.3 (aq)+8 MoO.sub.3 +H.sub.3 PO.sub.4 .fwdarw.Li.sub.4 H.sub.3
PMo.sub.8 V.sub.4 O.sub.40 (aq)
1091.28 grams granular V.sub.2 O.sub.5 (6.00 mole) was suspended in 2.0
liters distilled water in a Morton flask with overhead stirring and the
mixture was heated to about 60.degree. C. 443.34 grams Li.sub.2 CO.sub.3
chips (6.00 mole) was slowly added in portions to the rapidly stirred
mixture, causing CO.sub.2 liberation and dissolution of the V.sub.2
O.sub.5 to give and essentially homogeneous solution. The solution was
heated at the reflux for 60 minutes. The solution was then dark green due
to dissolved V.sup.IV which was originally present in the V.sub.2 O.sub.5.
Approximately 1 ml of 30% H.sub.2 O.sub.2 was added dropwise to the
mixture causing the dark, black-blue green color to fade, leaving a
slightly turbid lithium vanadate solution. The solution was maintained at
reflux for an additional 60 minutes to ensure the decomposition of excess
peroxide and then cooled to room temperature. The solution was clarified
by vacuum filtration to remove the small amount (.about.0.1 grams) of
brown solid which contained almost all the iron and silica impurities
originally present in the V.sub.2 O.sub.5. The clear, orange lithium
vanadate solution was then returned to a Morton flask, and 3454.56 grams
MoO.sub.3 (24.00 mole) was added with rapid overhead stirring. The mixture
was heated to about 60.degree. C. and 344.24 grams 85.4% (w/w) H.sub.3
PO.sub.4 (3.00 mole) was added. The mixture was heated at the reflux and
thereby converted to a clear, dark, burgundy-red solution. After 3 hours
at reflux, the homogenous burgundy-red solution was cooled to room
temperature and volumetrically diluted with distilled water to a total
volume of 10.00 liters, giving 0.30M {Li.sub.4 H.sub.3 PMo.sub.8 V.sub.4
O.sub.40 }, having -log[H.sup.+ ]=0.88.
Example 28
Preparation of 0.30M {Li.sub.7 PMo.sub.8 V.sub.4 O.sub.40 }
The polyoxoanion full salt solution 0.30M {Li.sub.7 PMo.sub.8 V.sub.4
O.sub.40 } was prepared analogously to 0.30M {Li.sub.4 PMo.sub.11
VO.sub.40 } (Example 3), according to the following reaction equations:
2 V.sub.2 O.sub.5 +2 Li.sub.2 CO.sub.3 .fwdarw.4 LiVO.sub.3 (aq)+2 CO.sub.2
.Arrow-up bold.
1.5 Li.sub.2 CO.sub.3 +4 LiVO.sub.3 (aq)+8 MoO.sub.3 +H.sub.3 PO.sub.4
.fwdarw.Li.sub.7 PMo.sub.10 V.sub.2 O.sub.40 +1.5 CO.sub.2 .Arrow-up
bold.+1.5 H.sub.2 O
The procedure was the same as in Example 27 with the exceptions that the
preparation was scaled to give 4.0 liter product solution (1.2 mole
dissolved polyoxoanion salt) and after the addition of the MoO.sub.3, the
mixture was heated to the reflux and an additional 133.00 grams Li.sub.2
CO.sub.3 chips (1.80 mole) was slowly added in portions to the stirred
suspension, before the addition of the H.sub.3 PO.sub.4.
Examples 29-31
Preparations of 0.30M {Li.sub.p H.sub.(7-p) PMo.sub.8 V.sub.4 O.sub.40 }
Solutions
The following phosphomolybdovanadic acid partial salt solution was prepared
by blending 0.30M {Li.sub.1.15 H.sub.5.85 PMo.sub.8 V.sub.4 O.sub.40 }
(Example 26) and 0.30M {Li.sub.4 H.sub.3 PMo.sub.8 V.sub.4 O.sub.40 }
(Example 27) in a (4-2.5):(2.5-1.15) volumetric ratio:
______________________________________
Example 29:
0.30 M {Li.sub.2.5 H.sub.4.5 PMo.sub.8 V.sub.4 O.sub.40 }
-log[H.sup.+ ] = 0.36
______________________________________
The following 0.30M {Li.sub.p H.sub.(7-p) PMo.sub.8 V.sub.4 O.sub.40 }
solutions were prepared by blending 0.30M 0.30M {Li.sub.4 H.sub.3
PMo.sub.8 V.sub.4 O.sub.40 } (Example 27) and 0.30M {Li.sub.7 PMo.sub.8
V.sub.4 O.sub.40 } (Example 28) in (7-p):(p-4) volumetric ratios:
______________________________________
Example 30:
0.30 M {Li.sub.4.1 H.sub.2.9 PMo.sub.8 V.sub.4 O.sub.40 }
-log[H.sup.+ ] = 0.99
Example 31:
0.30 M {Li.sub.4.7 H.sub.2.3 PMo.sub.8 V.sub.4 O.sub.40 }
-log[H.sup.+ ] = 1.48
______________________________________
Ethylene Reactions
Examples 32 through 56 show catalyst solutions within the scope of this
invention and their use in processes for oxidation of an olefin to a
carbonyl product within the scope of this invention, specifically
exemplifying processes for oxidation of ethylene to acetaldehyde. In each
of these examples, a palladium catalyst solution was prepared by the
addition of the indicated palladium salt, as well as any other indicated
solution components, to the indicated polyoxoanion oxidant solution. The
hydrogen ion concentration of each of the exemplified catalyst solutions
was the same as that of its parent polyoxoanion solution, as recited among
the preceding Examples.
The illustrated ethylene reactions were conducted in similarly equipped
stirred tank autoclave reactors having 300 ml internal volume and
fabricated of 316 stainless steel (Reactor #1), Hastelloy C (Reactor #2),
or titanium (Reactor #3). Each autoclave was equipped with a hollow shaft
stirring impeller fitted with a six bladed flat disk turbine, coaxial with
the cylindrical internal autoclave volume. The hollow shaft had a hole
high in internal volume for gas inlet and another at the impeller turbine
for efficient dispersion of the gas phase through the liquid phase. The
stirring impeller was magnetically coupled to magnets belted to a
rheostated direct current electric motor. Each autoclave was fitted with a
vertical baffle which extended along the internal wall through the
unstirred gas-liquid interface. Resistive electric heating elements were
jacketed to each autoclave body and were controlled by a proportioning
controller which monitored the liquid solution temperature via a
thermocouple. Volumetrically calibrated reservoirs for gas delivery were
connected to each autoclave via feed-forward pressure regulators.
The ethylene reactions were conducted in fed-batch mode, with a batch of
catalyst solution and a continuous regulated feed of ethylene from higher
pressure in the reservoir into the autoclave to maintain the set autoclave
pressure. Thermocouples and pressure transducers monitored the
temperatures and pressures of the reaction mixture in the autoclave and of
the ethylene in the reservoir, and a magnetic-sensing tachometer monitored
the impeller revolution rate. These transducers were all interfaced to a
computer system for continuous data acquisition as a function of time.
Reservoir volume, pressure, and temperature data were converted to moles
of ethylene in the reservoir using a non-ideal gas equation incorporating
the compressibility of ethylene.
For each exemplified ethylene reaction, 100 milliliters of the indicated
catalyst solution was charged to the autoclave and the gas phase in the
autoclave was changed to 1 atmosphere dinitrogen. The sealed autoclave was
heated to bring the stirring solution to the indicated reaction
temperature and the autogenic pressure at this temperature was noted. With
very gentle stirring of the solution, ethylene was regulated into the
autoclave to give a total autoclave pressure equal to the autogenic
pressure plus the indicated ethylene partial pressure. (With only very
gentle stirring of the liquid phase, gas-liquid mixing is almost nil and
the ethylene reaction is so severely diffusion limited that no detectable
reaction occurs. Gentle stirring, rather than no stirring, was provided to
avoid thermal gradients in the solution.) With the autoclave open to the
forward regulated total pressure from the reservoir, the reaction was
initiated by increasing the impeller stirring rate to provide efficient
dispersion of the gas through the liquid phase. The increase in stirring
rate occurred virtually instantaneously relative to the time scale of the
ensuing reaction. The reaction proceeded under constant pressure while
reservoir temperature and pressure data was collected. The decrease in
moles of ethylene in the reservoir was taken to correspond to the motes of
ethylene reacted.
For every exemplified ethylene reaction for which the acetaldehyde product
in the solution was quantitatively analyzed (by standard gas-liquid phase
chromatography procedures), the reaction selectivity to acetaldehyde was
.gtoreq.90%, typically .gtoreq.95%, and often .gtoreq.98%. Major
by-products were acetic acid and crotonaldehyde, which are secondary
products of acetaldehyde, by oxidation and condensation, respectively. The
amounts of these by-products increased and the amount of acetaldehyde
decreased with the amount of time the acetaldehyde-containing catalyst
solution spent at reaction temperature and subsequently at room
temperature after the reaction of ethylene to acetaldehyde reached
completion.
Statistically significant modest differences in ethylene reaction rates
were measured among the three different reactors for otherwise nominally
equivalent reactions. These differences were never more than 25%, usually
less, and are attributed to differences in the accuracies of the
temperature and ethylene pressure controls among the reactors. All recited
comparisons of results among the following Examples are drawn from
reactions conducted in the same reactor.
Volumetric ethylene reaction rate is reported as (millimole ethylene/liter
solution)/second, abbreviated mmol I.sup.-1 s.sup.-1. Palladium turnover
frequency, TF, is reported as (moles ethylene/mole palladium)/second,
abbreviated s.sup.-1, which is the volumetric ethylene reaction rate
divided by the palladium concentration. Ethylene conversion expressed as %
theory refers to the % utilization of the vanadium(V) capacity of the
solution according to reaction (12); it is 100 (moles ethylene
reacted)/(moles vanadium(V)/2). The palladium turnover number, TON, is
(total moles ethylene reacted/moles palladium).
Examples 32-35
Oxidation of Ethylene With 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 }
with Various Palladium Catalyst Concentrations
In each of these examples, a palladium catalyst solution was prepared by
dissolving palladium(II) acetate, Pd(CH.sub.3 CO.sub.2).sub.2, in 0.30M
{Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } (Example 22) at the millimolar
(mM) concentration indicated in Table 2. 100 milliliters of each catalyst
solution was reacted at 115.degree. C. with ethylene at 150 psi partial
pressure in Reactor #2 using an impeller stirring rate of about 2000 RPM.
The reactions were allowed to proceed until ethylene consumption ceased.
In each case, the measured ethylene consumption was close to theory (30.0
millimoles, corresponding to 3000 palladium turnovers). Table 2 lists the
palladium concentration, initial ethylene reaction rate, initial palladium
turnover frequency, and total ethylene consumption of each reaction.
TABLE 2
______________________________________
[Pd(II)] rate Pd TF C.sub.2 H.sub.4 reacted
Example
mM mmol l.sup.-1 s.sup.-1
s.sup.-1
mmoles % theory
______________________________________
32 0.045 3.2 70 27.4 91%
33 0.15 11.0 74 30.6 102%
34 0.15 10.8 72 30.9 103%
35 0.30 22.2 74 29.7 99%
______________________________________
FIG. 2 shows the ethylene reaction rates of Examples 32-35 plotted against
their palladium concentrations. The initial ethylene reaction rate is
linearly dependent on the palladium concentration; each reaction proceeded
with essentially the same palladium turnover frequency. Accordingly, the
gas-liquid mixing efficiency provided these reactions was sufficient for
the ethylene oxidation rate to be governed by the chemical kinetics of
catalysis. These reaction rates were not limited by ethylene dissolution
(mass transfer) into the catalyst solution. Each of the following
exemplified ethylene reactions was likewise provided mixing which was
confirmed to be sufficient for the ethylene oxidation rate to be governed
by chemical kinetics.
Example 36
Oxidation of Ethylene with 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2
O.sub.40 } Prepared with Sulfuric Acid and Having -log[H+]=1.00
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in the solution designated 0.30M {Na.sub.4.47
H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40 }+0.31 M Na.sub.1.48 H.sub.0.52
SO.sub.4 prepared according to the method of the Matveev patents as
adapted in Example 18.
100 milliliters of this catalyst solution was reacted at 120.degree. C.
with ethylene at 150 psi partial pressure in Reactor #3 using an impeller
stirring rate of about 2000 RPM. The ethylene consumption ceased within 10
minutes at 27.0 millimoles of ethylene, corresponding to 90% of the
theoretical vanadium(V) oxidizing capacity of the solution and 2700
turnovers of the palladium catalyst. The initial volumetric rate of
ethylene reaction was 3.0 mmol I.sup.-1 s.sup.-1, corresponding to a
palladium turnover frequency of 30 s.sup.-1.
The best exemplification in the Matveev patents (Matveev Example 6, see
Table 1 herein), at 88 psi ethylene and 110.degree. C., provided a
volumetric ethylene reaction rate of 0.670 mmol I.sup.-1 s.sup.-1, a
palladium turnover frequency of 0.335 s.sup.-1, and 150 turnovers of the
palladium catalyst (40% vanadium(V) conversion). The present example
provides 15 times greater ethylene reaction rate, 90 times greater
palladium turnover frequency, and 18 times greater palladium turnovers.
The present invention responsible for most of this multiplicatively
superior catalyst performance is the provision of efficient mixing of the
olefin with the catalyst solution in the process. Provided such mixing,
the kinetic capability of the catalyst solution in the inventive process
was revealed so unexpectedly exceptional compared to that indicated by the
processes of the Matveev patents and other background references.
Example 37
Oxidation of Ethylene with 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2
O.sub.40 }
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10
V.sub.2 O.sub.40 } (Example 15). This catalyst solution is free of sulfate
ions and has a hydrogen ion concentration of 0.10 mole/liter (-log[H.sup.+
]=1.00).
100 milliliters of this solution was reacted at 120.degree. C. with
ethylene at 150 psi partial pressure in Reactor #3 using an impeller
stirring rate of about 2000 RPM. (These are the same conditions as in
Example 36.) The reaction consumed 25.0 millimoles of ethylene with an
initial volumetric rate of reaction of 8.2 mmol I.sup.-1 s.sup.-1
corresponding to a palladium turnover frequency of 82 s.sup.-1.
Comparison with Example 36 shows that the ethylene reaction rate is greater
than 2.5 times faster with this catalyst solution, which is free of
sulfate ions, than with the corresponding catalyst solution having the
same hydrogen ion concentration, but prepared with sulfuric acid following
the method of the Matveev patents as adapted in Example 18.
Example 38
Oxidation of Ethylene with 0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2
O.sub.40 } Solution with Added Sodium Sulfate Salts
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in the solution designated 0.30M {Na.sub.4.47
H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40 }+0.31 M Na.sub.1.74 H.sub.0.26
SO.sub.4 having -log[H.sup.+ ]=1.00 prepared in Example 20.
100 milliliters of this solution was reacted at 120.degree. C. with
ethylene at 150 psi partial pressure in Reactor #3 using an impeller
stirring rate of about 2000 RPM. (These are the same conditions used in
Examples 36 and 37.) The reaction consumed 24.3 millimoles of ethylene
with an initial volumetric rate of reaction of 3.1 mmol I.sup.-1 s.sup.-1
corresponding to a palladium turnover frequency of 31 s.sup.-1.
This reaction rate is essentially identical to that obtained in Example 36
with the similar catalyst solution prepared with sulfuric acid. This
result confirms that the several fold greater ethylene reaction rate
obtained in Example 37 as compared to in Example 36 and in this Example is
due to the absence of sulfate ions in the catalyst solution of Example 37.
Examples 39-43
Oxidation of Ethylene with 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2
O.sub.40 } Solutions Having Various Hydrogen Ion Concentrations
In each of these examples, a palladium catalyst solution was prepared by
dissolving Pd(CH.sub.3 CO.sub.2).sub.2 to 0.10 mM concentration in the
0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 } solution
indicated in Table 3. 100 milliliters of each catalyst solution was
reacted at 120.degree. C. with ethylene at 150 psi partial pressure in
Reactor #3 using an impeller stirring rate of about 2000 RPM, until
ethylene consumption ceased. (These are the same reaction conditions used
in Examples 36 through 38.) In some of these examples, the reaction was
repeated with 100 milliliters virgin catalyst solution using an impeller
stirring rate of about 3000 RPM. Table 3 lists the sodium countercation
balance p and -log[H.sup.+ ] of the phosphomolybdovanadate solution, the
initial ethylene reaction rate and palladium turnover frequency, and the
total ethylene consumption.
TABLE 3
__________________________________________________________________________
rate
{Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 }
mmol
Pd TF
C.sub.2 H.sub.4 reacted
Example
p Example
-log[H.sup.+ ]
RPM l .multidot. s
s.sup.-1
mmoles
% theory
__________________________________________________________________________
39 2 11 0.18 2050
10.4
104 32.9 110%
3010
9.7 97 31.8 106%
40 4 13 0.69 2980
9.6 96 28.9 96%
2060
9.2 92 28.7 96%
41 4.40 14 0.91 2030
8.6 86 28.0 93%
3020
9.1 91 27.3 91%
37 4.47 15 1.00 2050
8.2 82 25.1 84%
42 4.80 16 1.43 2050
4.8 48 25.0 83%
43 4.94 17 1.96 2050
0.7 7 23.0 77%
__________________________________________________________________________
FIG. 1 shows the initial palladium turnover frequencies of the examples
listed in Table 3 plotted against the -log[H.sup.+ ] of their catalyst
solutions. The greatest palladium catalyst activities were discovered only
at hydrogen ion concentrations greater than 0.10 moles/liter
(-log[H.sup.+]<1.0). At the hydrogen ion concentration of 0.10 moles/liter
-log[H.sup.+ ]=1.0), the initial palladium catalyst activity is already
significantly reduced from the higher activities achieved at greater
hydrogen ion concentrations, and it decreases precipitously as the
concentration of hydrogen ions is decreased below 0.10 moles/liter
(-log[H.sup.+ ]>1.0).
Each of Examples 39, 40, and 41 shows that the measured initial ethylene
reaction rate is not significantly different between otherwise identical
reactions using impeller stirring rates of about 2000 RPM and about 3000
RPM. This confirms that these reaction rates are not limited by
dissolution (mass transfer) of ethylene into the catalyst solution, but
represent the maximal chemical kinetics capabilities of these specific
catalyst solutions under these specific temperature and pressure
conditions.
The examples listed in Table 3 also show that more effective utilization of
the total vanadium(V) oxidizing capacity in the polyoxoanion solution was
discovered to be achievable at hydrogen ion concentrations greater than
0.10 moles/liter. At such increasing hydrogen ion concentrations, the
ethylene consumption vs. theory on vanadium(V) (according to reaction
(12)) approached and even exceeded 100% (suggesting partial reduction of
molybdenum(VI) to molybdenum(V)). At decreasing hydrogen ion
concentrations less than 0.10 the ethylene consumption of the solution was
significantly reduced below the theoretical capacity.
The exemplified reactions listed in Table 3 also manifested the pronounced
benefit of hydrogen ion concentrations greater than 0.10 moles/liter for
preserving the initial activity of the palladium(II) catalyst. At hydrogen
ion concentrations increasingly greater than 0.10 mole/liter, the initial
ethylene reaction rate was increasingly sustained to greater ethylene
conversions (and correspondingly decreasing vanadium(V) concentrations).
At hydrogen ion concentrations decreasingly less than 0.10 mole/liter, the
ethylene reaction rate increasingly decelerated from the initial rate as a
function of the ethylene conversion. This rate decay ultimately led to
zero rate and the increasingly less-than-stoichiometric ethylene
consumptions according to reaction (12) measured for catalyst solutions
having hydrogen ion concentrations increasingly greater than 0.10
moles/liter (see Table 3).
Improved preservation of palladium catalyst activity in catalyst solutions
and processes wherein the hydrogen ion concentration is greater than 0.10
moles/liter is also evidenced in processes which repeatedly cycle the
catalyst solution between ethylene reactions and dioxygen reactions
(two-stage mode). At hydrogen ion concentrations increasingly greater than
0.10 moles/liter, the ethylene reaction rate is increasingly sustained
from cycle to cycle. In contrast, at hydrogen ion concentrations
decreasingly less than 0.10 moles/liter, the ethylene reaction rate
increasingly decelerates from cycle to cycle until only a substantially
depressed rate is sustained or the reaction effectively ceases.
Example 44
Oxidation of Ethylene with 0.317M {H.sub.4.9 PMo.sub.10.1 V.sub.1.9
O.sub.40 }
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.317M {H.sub.4.9 PMo.sub.10.1 V.sub.1.9
O.sub.40 } (Example 10), having-log[H.sup.+ ]=-0.07.
100 milliliters of this solution was reacted at 120.degree. C. with
ethylene at 150 psi partial pressure in Reactor #3 using an impeller
stirring rate of about 2000 RPM. (The same conditions as for the Examples
in Table 3.) The reaction consumed 34.1 millimoles of ethylene with an
initial volumetric reaction rate of 108 mmol I.sup.-1 s.sup.-1,
corresponding to a palladium turnover frequency of 108 s.sup.-1. The
reaction was repeated with 100 milliliters virgin catalyst solution using
an impeller stirring rate of about 3000 RPM. This reaction consumed 33.2
millimoles of ethylene with an initial volumetric reaction rate of 9.4
mmol I.sup.-1 s.sup.-1, corresponding to a palladium turnover frequency of
94 s.sup.-1. These results are comparable to those obtained with 0.30M
{Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 } in Example 39.
This example demonstrates that phosphomolybdovanadic free acids are useful
in the inventive catalyst solutions and processes without the addition of
sulfuric acid, in contrast to the indications of the Matveev patents.
Example 45
Oxidation of Ethylene with 0.30M {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2
O.sub.40 } Prepared with Sulfuric Acid to -log[H+]=0.18
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in the solution designated 0.30M {Na.sub.2
H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 }+0.67M Na.sub.1.8 H.sub.0.2 SO.sub.4
prepared with sulfuric acid in Example 19.
100 milliliters of this catalyst solution was reacted at 120.degree. C.
with ethylene at 150 psi partial pressure in Reactor #3 using an impeller
stirring rate of about 3000 RPM. (These reaction conditions are
essentially the same as for Examples 36 and 39). The ethylene reaction
ceased with 21.9 millimoles of ethylene consumed, corresponding to
reduction of 73% of the vanadium(V) oxidizing equivalents in the solution.
The initial volumetric reaction rate was 6.1 mmol I.sup.-1 s.sup.-1,
corresponding to a palladium turnover frequency of 61 s.sup.-1. This
result is plotted in FIG. 1.
This ethylene reaction rate is about twice that of Example 36, which used
the corresponding polyoxoanion solution prepared with sulfuric acid to
-log[H.sup.+ ]=1.0. This comparison demonstrates that the ethylene
reaction rate is markedly increased at hydrogen ion concentrations greater
than 0.10 moles/liter (-log[H.sup.+ ]<1.0) even among catalyst solutions
containing sulfate ions, and even when additional sulfuric acid is added
to achieve the greater hydrogen ion concentration.
The ethylene reaction rate of the present Example is only about 60% that of
Example 39, which used 0.30M {Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40
}, the corresponding polyoxoanion solution having a comparable hydrogen
ion concentration, but free of sulfuric acid and sulfate ions. This
comparison demonstrates that the addition of sulfuric acid, and its
resulting sulfate ions, depresses the ethylene reaction rate even among
catalyst solutions having hydrogen ion concentrations greater than 0.10
moles/liter.
Comparison with Example 39 also shows a curtailed ethylene reaction
capacity, significantly below the theoretical vanadium(V) oxidizing
capacity, for the sulfate-containing catalyst solution of the present
Example.
Example 46
Oxidation of Ethylene with 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 }
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 } (Example 24), having -log[H.sup.+ ]=0.45.
100 milliliters of this solution was reacted at 120.degree. C. with
ethylene at 150 psi partial pressure in Reactor #3 using an impeller
stirring rate of about 2000 RPM. The reaction consumed 42.6 millimoles of
ethylene (95% of theory on vanadium(V)) with an initial volumetric rate of
reaction of 9.4 mmol I.sup.-1 s.sup.-1 corresponding to a palladium
turnover frequency of 94 s.sup.-1.
This reaction rate is comparable to those of Examples 39 and 40 in Table 3
for reactions of 0.30M {Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 } and
0.30M {Na.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } in the same reactor under
the same reaction conditions with the same palladium catalyst
concentration. These {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 }
catalyst solutions have hydrogen ion concentrations which bracket that of
the present 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 } catalyst
solution. This comparison shows that the palladium catalyst activity is
not significantly dependent on the vanadium content of the
phosphomolybdovanadate in catalyst solutions having comparable hydrogen
ion concentrations.
Another 100 milliliters of the 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 } palladium catalyst solution was reacted with ethylene under
nominally the same temperature and pressure conditions in Reactor #2. The
reaction consumed 45.7 millimoles of ethylene (102% of theory on
vanadium(V)) with an initial volumetric rate of reaction of 11.6 mmol
I.sup.-1 s.sup.-1 corresponding to a palladium turnover frequency of 116
s.sup.-1. (Such a relative difference in measured reaction rates between
the indicated Reactors for nominally the same reaction conditions was
confirmed reproducibly with other catalyst solutions.)
Examples 47-49
Oxidation of Ethylene with 0.30M {Li.sub.p H.sub.(7-p) PMo.sub.8 V.sub.4
O.sub.40 } Solutions Having Various Hydrogen Ion Concentrations
In each of these examples, a palladium catalyst solution was prepared by
dissolving Pd(CH.sub.3 CO.sub.2).sub.2 to 0.10 mM concentration in the
0.30M {Li.sub.p H.sub.(7-p) PMo.sub.8 V.sub.4 O.sub.40 } solution
indicated in Table 4. 100 milliliters of each catalyst solution was
reacted at 120.degree. C. with ethylene at 150 psi partial pressure in
Reactor #2 using an impeller stirring rate of about 2000 RPM, until
ethylene consumption ceased. Table 4 lists the lithium countercation
balance p and -log[H.sup.+ ] of the phosphomolybdovanadate solution, the
initial ethylene reaction rate and palladium turnover frequency, and the
total ethylene consumption.
TABLE 4
__________________________________________________________________________
rate
{Li.sub.p H.sub.(7-p) PMo.sub.8 V.sub.4 O.sub.40 }
mmol
PdTF
C.sub.2 H.sub.4 reacted
Example
p Example
-log[H.sup.+ ]
l .multidot. s
s.sup.-1
mmoles
% theory
__________________________________________________________________________
47 2.5 29 0.34 11.3
113 56.6 94%
48 4.1 30 0.99 8.1 81 50.3 84%
49 4.7 31 1.48 4.1 41 40.0 67%
__________________________________________________________________________
These examples again demonstrate that greater palladium catalyst activities
and greater utilization of the vanadium(V) oxidizing equivalents are
provided by the inventive catalyst solutions and processes wherein the
concentration of hydrogen ions is greater than 0.10 moles/liter
(-log[H.sup.+ ]<1.0). These reactions also manifested increasingly better
sustained initial reaction rates to greater ethylene conversions at
hydrogen ion concentrations increasingly greater than 0.10 moles/liter.
Example 50
Oxidation of Ethylene with 0.30M {Li.sub.2.67 H.sub.1.33 PMo.sub.11 V.sub.1
O.sub.40 }
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Li.sub.2.67 H.sub.1.33 PMo.sub.11
V.sub.1 O.sub.40 } (Example 8), having -log[H.sup.+ ]=0.37.
100 milliliters of this solution was reacted at 120.degree. C. with
ethylene at 150 psi partial pressure in Reactor #2 using an impeller
stirring rate of about 2000 RPM. The reaction consumed 22.0 millimoles of
ethylene. This is 147% of theory on the vanadium(V) oxidizing equivalents
and indicates significant reduction of the molybdenum(VI) in the
PMo.sub.11 V.sub.1 O.sub.40.sup.4- anion as well. The initial volumetric
rate of reaction of 12.4 mmol I.sup.-1 s.sup.-1 corresponding to a
palladium turnover frequency of 124 s.sup.-1.
Example 51
Oxidation of Ethylene with 0.30M {Li.sub.3.24 H.sub.1.76 PMo.sub.10 V.sub.2
O.sub.40 }
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Li.sub.3.24 H.sub.1.76P Mo.sub.10
V.sub.2 O.sub.40 } (Example 23), having -log[H.sup.+ ]=0.37.
100 milliliters of this solution was reacted at 120.degree. C. with
ethylene at 150 psi partial pressure in Reactor #2 using an impeller
stirring rate of about 2000 RPM. The reaction consumed 27.2 millimoles of
ethylene (91% of theory on vanadium(V)) with an initial volumetric rate of
reaction of 11.9 mmol I.sup.-1 s.sup.-1 corresponding to a palladium
turnover frequency of 119 s.sup.-1.
Example 52
Oxidation of Ethylene with 0.30M {Li.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 }
A catalyst solution was prepared containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Li.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 } (Example 25), having -log[H.sup.+ ]=0.38.
In each of four tests, a 100 milliliter volume of this solution was reacted
at 120.degree. C. with ethylene at 150 psi partial pressure in Reactor #2
using an impeller stirring rate of about 2000 RPM. The individual test
results are listed in Table 5. The average ethylene consumption was 45.5
millimoles (101% of theory on vanadium(V)). The average initial volumetric
rate of reaction was 11.6 mmol I.sup.-1 s.sup.-1 corresponding to a
palladium turnover frequency of 116 s.sup.-1.
Table 5 collects results from preceding Examples for reactions of ethylene
with various 0.30M {A.sub.p H.sub.(3+n-p) PMo.sub.(12-n) V.sub.n O.sub.40
} palladium catalyst solutions having comparable hydrogen ion
concentrations, all conducted in Reactor #2 under the same reaction
conditions.
TABLE 5
__________________________________________________________________________
rate
{A.sub.p H.sub.(3+n-p) PMo.sub.(12-n) V.sub.n O.sub.40 }
mmol
PdTF
C.sub.2 H.sub.4 reacted
Example
A p n -log[H.sup.+ ]
l .multidot. s
s.sup.-1
mmoles
% theory
__________________________________________________________________________
50 Li 2.67 1 0.37 12.4
124 22.0 147
51 Li 3.24 2 0.37 11.9
119 27.2 91
52 Li 3 3 0.38 11.8
118 46.1 102
11.3
113 44.9 100
11.9
119 46.1 102
11.4
114 45.0 100
47 Li 2.5 4 0.36 11.3
113 56.6 94
46 Na 3 3 0.45 11.6
116 45.7 102
__________________________________________________________________________
The reactions listed in Table 5 exhibited comparable initial ethylene
reaction rates, indicating that the palladium(II) catalyst activity is not
significantly dependent on the average vanadium content, n, of the
phosphomolybdovanadate anions or on the vanadium(V) concentration among
these catalyst solutions having comparable hydrogen ion concentrations.
These rate measurements spanned solutions having vanadium(V)
concentrations from 0.30 g-atoms/liter to 1.2 g-atoms/liter at constant
polyoxoanion concentration. These rate measurements spanned solutions
having average vanadium contents from n=1, which contains substantially
only the PMo.sub.11 VO.sub.40.sup.4- anion, to n=4, which contains a
distribution of H.sub.y PMo.sub.(12-x) V.sub.x O.sub.40.sup.(3+x-Y)-
anions including substantial concentrations of anions with x>4. These
results indicate that the phosphomolybdovanadate anions do not coordinate
palladium(II) under the reaction conditions, as the different
phosphomolybdovanadates do not give different palladium catalyst activity.
Palladium(II) catalytic activity independent of vanadium(V) concentration
was also evidenced in exemplified reactions provided hydrogen ion
concentrations greater than 0.10 mole/liter by their ethylene reaction
rate over the course of the reaction, which did not decelerate in
proportion to the decreasing vanadium(V) concentration.
As these ethylene reaction rates are dependent on the palladium(II)
concentration and substantially independent of the vanadium(V)
concentration and specific phosphomolybdovanadate identity, the superior
olefin oxidation reactivity provided by hydrogen ion concentrations
greater than 0.10 mole/liter in the inventive catalyst solutions and
processes is attributed to a favorable influence of such hydrogen ion
concentrations on the palladium(II) activity for olefin oxidation
according to reaction (14). Accordingly, a capability for superior
palladium catalyst activity may be provided in a solution of any
polyoxoanion comprising vanadium(V) wherein the concentration of hydrogen
ions is greater than 0.10 mole/liter (provided, of course, that the
constitution and efficacy of the specific vanadium(V) oxidant is not
detrimentally affected by such hydrogen ion concentration).
In such acidic aqueous solution in the absence of coordinating ligands or
anions, palladium(II) is thought to exist as tetraaquopalladium(II),
Pd(H.sub.2 O).sub.4.sup.2+. The precipitously decreasing ethylene reaction
rate for catalyst solutions at decreasing hydrogen ion concentrations of
0.10 mole/liter and less (-log[H.sup.+ ].gtoreq.-1) may be attributed to
the double deprotonation of Pd(H.sub.2 O).sub.4.sup.2+, with pK.sub.a 's
about 2, to less active hydroxo species according to reaction (16). The
log[rate] vs. -log[H.sup.+ ] slope between the reactions of Examples 42
and 43, with -log[H.sup.+ ] at 1.43 and 1.96 respectively, is -1.5,
consistent with the removal of more than one proton from the active
palladium catalyst.
The superior olefin oxidation reactivity in the inventive catalyst
solutions and processes essentially free of sulfuric acid and sulfate ions
must likewise be attributed to a favorable influence of omitting sulfuric
acid and sulfate ions on the palladium(II)-olefin reaction. Palladium(II)
is known not to coordinate sulfate ions in water, so it is doubtful that
sulfate directly influences the palladium(II) catalyst. More likely,
sulfate salts decrease ("salt out") the solubility of the olefin in the
aqueous solution and thereby decrease the concentration of dissolved
olefin available for reaction with palladium(II). Accordingly, superior
olefin oxidation rates may be expected for any aqueous catalyst solution
essentially free of sulfuric acid and sulfate ions. Accordingly, a
capability for superior olefin oxidation rates may be provided in any
polyoxoanion solution which is essentially free of sulfuric acid and
sulfate ions.
Example 53
Oxidation of Ethylene with 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 }
A catalyst solution was prepared containing 0.10 mM Na.sub.2 PdCl.sub.4
dissolved in 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 } (Example
24), having -log[H.sup.+ ]=0.45 and 0.40 mM chloride ions.
100 milliliters of this solution was reacted at 115.degree. C. with
ethylene at 150 psi partial pressure in Reactor #3 using an impeller
stirring rate of about 2000 RPM. The reaction consumed 40.5 millimoles of
ethylene (90% of theory on vanadium(V)) with an initial volumetric rate of
reaction of 8.7 mmol I.sup.-1 s.sup.-1 corresponding to a palladium
turnover frequency of 87 s.sup.-1.
Example 54
Oxidation of Ethylene with 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 } with Added Sodium Sulfate Salts
A sulfate-containing stock solution was prepared by dissolving Na.sub.2
SO.sub.4 to 1.5M concentration in a volume of the catalyst solution of
Example 53. Another was prepared by dissolving NaHSO.sub.4
.multidot.H.sub.2 O to 1.5M concentration in another volume of the same
catalyst. These two stock solutions were blended in a 7:3 ratio to obtain
a catalyst solution with the same -log[H.sup.+ ] measurement as the parent
catalyst solution of Example 53. This solution is designated 0.30M
{Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 }+1.5M Na.sub.1.7 H.sub.0.3
SO.sub.4 containing 0.10 mM Na.sub.2 PdCl.sub.4.
100 milliliters of this solution was reacted with ethylene under the same
conditions used in Example 53. The ethylene reaction ceased with 33.0
millimoles of ethylene consumed (73% of theory on vanadium(V)). The
initial volumetric rate of reaction was 3.1 mmol I.sup.-1 s.sup.-1
corresponding to a palladium turnover frequency of 31 s.sup.-1.
Comparison with Example 53 shows that the presence of the sulfate ions in
the present Example results in a reaction rate less than 40% of that
obtained in their absence. The present Example also shows a curtailed
ethylene reaction capacity, significantly below the theoretical
vanadium(V) oxidizing capacity, for this sulfate-containing catalyst
solution.
Example 55
Oxidation of Ethylene with 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 O.sub.40 }
with 25 mM Chloride
The procedure was the same as for Example 53 with the exception that 2.46
millimole NaCl was added in the 100 milliliters of catalyst solution which
was reacted with ethylene. The chloride concentration of this solution was
25 mM.
The reaction consumed 43.7 millimoles of ethylene (97% of theory on
vanadium(V)) with an initial volumetric rate of reaction of 3.4 mmol
I.sup.-1 s.sup.-1 corresponding to a palladium turnover frequency of 34
s.sup.-1.
Example 56
Oxidation of Ethylene With 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 } with 25 mM Chloride and Added Sodium Sulfate Salts
The procedure was the same as for Example 54 with the exception that 2.46
millimole NaCl was added in the 100 milliliters of sulfate-containing
catalyst solution which was reacted with ethylene. The solution contained
25 mM chloride and 1.5M sulfate ions, having the same -log[H.sup.+ ] as
the catalyst solution of Example 55.
The ethylene reaction ceased with 33.2 millimoles of ethylene consumed (74%
of theory on vanadium(V)). The initial volumetric rate of reaction was 1.8
mmol I.sup.-1 s.sup.-1 corresponding to a palladium turnover frequency of
18 s.sup.-1.
Comparison with Example 55 again shows that the presence of the sulfate
ions decreases the ethylene reaction rate, in this case to about 50% of
that obtained in the absence of sulfate. The present Example also again
shows curtailed ethylene reaction capacity, significantly below the
theoretical vanadium(V) oxidizing capacity, in the presence of sulfate.
Butene Reaction
The following example shows a catalyst solution within the scope of this
invention used in a process for the oxidation of 1-butene to 2-butanone
within the scope of this invention. The 1-butene reaction was conducted in
a 300 ml Hastelloy C stirred tank autoclave reactor equipped similarly to
the previously described reactors used for the preceding examples of
ethylene reactions. The volumetrically calibrated 1-butene reservoir and
its feed lines to the reactor were heated to keep the contained 1-butene
in the gas state. The reaction was conducted in fed-batch mode by the
methods described for the ethylene reactions.
Example 57
Oxidation of 1-butene with 0.30M {Li.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 }
A catalyst solution was prepared containing 0.60 mM Pd(CH.sub.3
CO.sub.2).sub.2 and 30 mM LiCl dissolved in 0.30M {Li.sub.3 H.sub.3
PMo.sub.9 V.sub.3 O.sub.40 } (Example 25), having -log[H.sup.+ ]=0.38.
150 milliliters of this catalyst solution was reacted at 130.degree. C.
with 1-butene at 200 psi partial pressure using an impeller stirring rate
of about 2000 RPM. The initial volumetric rate of 1-butene reaction was
5.9 mmol I.sup.-1 s.sup.-1, corresponding to a palladium turnover
frequency of 10 s.sup.-1. The stirring was stopped 60 seconds after its
initiation to stop the reaction. 26 millimoles of 1-butene were consumed
within that time, corresponding to 39% utilization of the vanadium(V)
oxidizing capacity of the solution. The predominant product of this
1-butene reaction is 2-butanone.
Dioxygen Reactions
Examples 58 through 67 show processes within the scope of this invention
for oxidation of vanadium(IV) and for regeneration of a polyoxoanion
oxidant comprising vanadium by reaction of an aqueous solution of
vanadium(IV) and a polyoxoanion with dioxygen.
The illustrated dioxygen reactions were conducted in the same autoclave
reactors used for the preceding Examples of ethylene reactions. The
autoclave reactors were equipped as previously described, with the
exception, when indicated, that the single vertical baffle was replaced
with a cage of four vertical baffles, at 90.degree. relative positions
around the cylindrical internal autoclave wall, to provide more turbulent
gas-liquid mixing at a set impeller stirring speed. The dioxygen reactions
were conducted in fed-batch mode with a batch of reduced
vanadium-polyoxoanion solution and a continuous forward regulated feed of
dioxygen from higher pressure in a volumetrically calibrated reservoir
into the autoclave. Reactions were monitored and data acquired over time
as previously described for the ethylene reactions. Reservoir volume,
pressure, and temperature data were converted to mole of dioxygen in the
reservoir using the ideal gas equation.
For each exemplified dioxygen reaction, the indicated vanadium-polyoxoanion
solution was charged to the autoclave and the vanadium(V) was reduced to
vanadium(IV) in the autoclave prior to the reaction with dioxygen. Except
when otherwise indicated, the vanadium-polyoxoanion solution included a
palladium(II) catalyst and was reduced by reaction with carbon monoxide.
Palladium catalyzes the oxidation of carbon monoxide to carbon dioxide by
the vanadium(V), according to the following equation:
##STR4##
This is analogous to the oxidation of olefins to carbonyl compounds,
illustrated in reaction (12) for the oxidation of ethylene to
acetaldehyde. Carbon dioxide is readily removed from the catalyst solution
prior to the dioxygen reaction. The use of carbon monoxide as reductant
preceding dioxygen reactions, instead of an olefin, facilitated the
measurement volumetric dioxygen reaction rates and dioxygen reaction
capacities characteristic of the vanadium(IV)-polyoxoanion solutions under
the specific reaction conditions, as it avoids any potential confounding
influences of olefin oxidation products on the data without the
inconvenience of completely removing them from the aqueous solutions prior
to the dioxygen reaction. Multiple cycles of carbon monoxide and dioxygen
reactions could also be conducted with a single batch of catalyst without
inconvenient removal of olefin oxidation products.
To reduce a catalyst solution with carbon monoxide in the autoclave, the
gas phase over the solution in the sealed autoclave was first changed to 1
atmosphere dinitrogen. The stirring solution was then heated to the
desired reaction temperature, typically 120.degree. C. Carbon monoxide was
regulated into the autoclave, to give a total autoclave pressure of at
least 150 psig, typically 250 psig. The catalyst solution was reduced by
increasing the impeller stirring speed sufficiently to provide efficient
dispersion of the gas through the liquid phase for at least 10 minutes.
The reaction solution was then cooled to room temperature, the autoclave
gas pressure was vented, and the gas phase in the autoclave was replaced
with 1 atmosphere dinitrogen. This involved several cycles of dispersing
dinitrogen under pressure through the liquid phase and venting to 1
atmosphere to remove essentially all dissolved carbon dioxide.
When reduced in this way with excess carbon monoxide, the catalyst solution
become fully reduced. That is, all the vanadium(V) is reduced to
vanadium(IV). Fractionally reduced catalyst solutions were prepared by
fully reducing the corresponding volume fraction of the solution with
excess carbon monoxide, following which the remaining volume fraction of
oxidized solution was deaerated and added into the autoclave under
dinitrogen.
For each exemplified dioxygen reaction, with 100 milliliters of the
indicated reduced solution in the sealed autoclave under 1 atmosphere
dinitrogen, the autoclave was heated to bring the stirring reduced
solution to the indicated reaction temperature and the autogenic pressure
at this temperature was noted. With very gentle stirring of the solution,
dioxygen was regulated into the autoclave to give a total autoclave
pressure equal to the autogenic pressure plus the indicated dioxygen
partial pressure. (With only very gentle stirring of the liquid phase,
gas-liquid mixing is almost nil and the dioxygen reaction is so severely
diffusion limited that no detectable reaction occurs. Gentle stirring,
rather than no stirring, was provided to avoid thermal gradients in the
solution.) With the autoclave open to the forward regulated pressure from
the reservoir, the reaction was initiated by increasing the impeller
stirring speed to provide efficient dispersion of the gas through the
liquid phase. The increase in stirring rate occurred virtually
instantaneously relative to the time scale of the ensuing reaction. The
reaction proceeded under constant pressure while reservoir temperature and
pressure data was collected. The decrease in moles of dioxygen in the
reservoir was taken to correspond to the moles of dioxygen reacted.
Example 58
Oxidation of Reduced 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } With
Dioxygen at Various Gas-Liquid Mixing Efficiencies
100 milliliters of a catalyst solution containing 0.15 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40
} (Example 22), having -log[H.sup.+ ]=0.63, was charged to Reactor #2
equipped with a single vertical baffle and alternately fully reduced with
carbon monoxide and reacted at 120.degree. C. with dioxygen at 27 psi
partial pressure at the impeller stirring rates indicated in Table 6. The
dioxygen reactions were allowed to proceed until dioxygen consumption
ceased. For each reaction, the measured dioxygen consumption was close to
theory for complete oxidation of the vanadium content of the solution,
100% as vanadium(IV), according to reaction (13): 15.0 millimoles dioxygen
to oxidized 60 mg-atoms vanadium(IV). Table 6 lists the impeller stirring
rate, initial dioxygen reaction rate, and total dioxygen consumption for
the individual reactions. These dioxygen reaction rates are plotted
against the impeller stirring speed in FIG. 3.
TABLE 6
______________________________________
rate O.sub.2 reacted
RPM mmol l.sup.-1 s.sup.-1
mmoles % theory
______________________________________
1020 0.4 15.0 100
1640 2.4 14.8 99
1960 3.7 15.1 101
2630 5.8 14.2 95
3280 7.8 14.5 97
______________________________________
Example 59
Oxidation of Reduced 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 }
With Dioxygen at Various Gas-Liquid Mixing Efficiencies
100 milliliters of a catalyst solution containing 0.10 mM Na.sub.2
PdCl.sub.4 and 4.60 mM NaCl dissolved in 0.30M {Na.sub.3 H.sub.3 PMo.sub.9
V.sub.3 O.sub.40 } (Example 24), having -log[H.sup.+ ]=0.45, was charged
to Reactor #2 equipped with a cage of four vertical baffles and
alternately fully reduced with carbon monoxide and reacted at 110.degree.
C. with dioxygen at 25 psi partial pressure at the impeller stirring rates
indicated in Table 7. The dioxygen reactions were allowed to proceed until
dioxygen consumption ceased. Table 7 lists the impeller stirring rate,
initial dioxygen reaction rate, and total dioxygen consumption for the
individual dioxygen reactions. These dioxygen reaction rates are plotted
against the impeller stirring speed in FIG. 3.
TABLE 7
______________________________________
rate O.sub.2 reacted
RPM mmol l.sup.-1 s.sup.-1
mmoles % theory
______________________________________
1230 2.6 not available
1480 4.5 24.9 111
2030 9.4 25.8 115
2050 9.8 23.2 103
2810 14.0 not available
______________________________________
Example 60
Oxidation of Reduced 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 }
with Dioxygen at Various Gas-Liquid Mixing Efficiencies
The procedure was the same as in Example 59 with the exception that the
reactions were conducted in Reactor #3 equipped with a cage of four
vertical baffles and the dioxygen partial pressure was nominally 36 psi.
Table 8 lists the impeller stirring rate, initial dioxygen reaction rate,
and total dioxygen consumption for the individual dioxygen reactions.
These dioxygen reaction rates are plotted against the impeller stirring
speed in FIG. 3.
TABLE 8
______________________________________
rate O.sub.2 reacted
RPM mmol l.sup.-1 s.sup.-1
mmoles % theory
______________________________________
1130 1.7 23.6 105
2050 5.4 24.5 111
3050 10.0 23.3 104
______________________________________
FIG. 3 plots the initial dioxygen reaction rates of Examples 58, 59, and 60
against impeller stirring speed. The reaction rates in each Example are
linearly dependent on the stirring rate up to the highest stirring rates
available in the reactors. Accordingly, these initial dioxygen reaction
rates are limited by the rate of dioxygen dissolution (mass transfer)into
the vanadium(V)-polyoxoanion solution, which increases as the gas-liquid
mixing efficiency in the reactor is improved by increased stirring speed.
Differences in reaction rates among these three Examples manifest
differences in baffling and impeller efficiency among the reactors which
influence the gas-liquid mixing efficiency obtained as a function of the
impeller stirring rate.
Additionally, these reactions proceed at near constant rate--the rate does
not decelerate in proportion to the decreasing vanadium(IV)
concentration--up to high conversion of the vanadium(IV) to vanadium(V),
usually >80% conversion, typically to .about.90% conversion. The intrinsic
kinetic reactivity of these concentrated vanadium(IV) solutions at these
temperatures under these conditions exceeds the rate at which dioxygen can
be dissolved into solution, until the vanadium(IV) concentration is
substantially depleted by the reaction.
The results from Examples 58, 59, and 60 each indicate, by
back-extrapolation that significant reaction rates could be obtained only
at any stirring rates greater than about 800 RPM in these reactors. This
threshold is taken to indicate the lowest stirring rate at which gas could
be successfully suctioned down the hollow impeller shaft as far as the
impeller for efficient dispersion through the liquid phase.
The best exemplification in the Matveev patents (Matveev Example 6, see
Table 1 herein) provided a volumetric dioxygen reaction rate of 0.335 mmol
I.sup.-1 s.sup.-1 at 110.degree. C. with 51 psi dioxygen with a solution
said to have "pH . . . adjusted to 1.0" by H.sub.2 SO.sub.4 during its
preparation in oxidized form. This rate just approaches the slowest
dioxygen reaction rate measured in the preceding examples at lower
pressure. (Gas-liquid mass transfer limited reaction rates are directly
dependent on the pressure of the reacting gas and little affected by
temperature.) The highest reaction rates achieved in the preceding
examples is over 40 times greater than this best exemplification in the
Matveev patents, again with lower pressure. The present invention most
responsible for this multiplicatively superior reaction performance is the
provision of efficient mixing of the dioxygen with the reduced
vanadium-polyoxoanion solution in the process. Provided such mixing, the
reactivity of the vanadium(IV)-polyoxoanion solution in the inventive
process was revealed so unexpectedly exceptional compared to that
indicated by the processes of the Matveev patents and other background
references. Even greater dioxygen reaction rates can be obtained in even
more efficient gas-liquid mixing reactors.
The Matveev patents state that the "pH" of their solutions is preferably at
1.0 and, "At lower pH values, the rate of the oxygen reaction is
appreciably diminished." Similarly, Koordinatsionnaya Khimiya, vol. 3,
(1977), pp. 51-58 (English translation edition pp. 39-44 shows a graph
with a maximum rate of only 0.57 mmol I.sup.-1 s.sup.-1 at about "pH" 3
which declines to almost negligible rate by "pH" 1. Attributions of
diminished rates to lower "pH" values obligatorily implies that the
diminished rates are limited by the chemical kinetics of the reaction.
(Rates which are limited by the chemical kinetics cannot be increased by
increased gas-liquid mixing efficiency.) In contrast to this teaching, and
as demonstrated in the preceding and following Examples, the present
invention provides processes for oxidizing vanadium(IV) in polyoxoanion
solutions, even solutions having -log[H.sup.+ ]<1.0, at rates
multiplicatively faster than the processes disclosed reported in the
Matveev patents for solutions said to have "pH 1.0".
Example 61
Oxidation of Reduced 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } with
Dioxygen
The procedure of Example 58 was used for reactions of fully reduced 0.30M
{Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } at 120.degree. C. with dioxygen
at 28.+-.1 psi partial pressure in Reactor #2 equipped with a single
vertical baffle using impeller stirring rates of 2000.+-.100 RPM. Three
separate 100 milliliter solution samples were each reduced and reacted
with dioxygen two times. Between the tests on the separate solution
samples, the reactor was disassembled, cleaned, and reassembled several
times for other experiments. Reactor disassembly and reassembly was found
to be a source of variability in the mass-transfer limited reaction rates
as are variations in dioxygen partial pressure and impeller stirring
speed. The average initial dioxygen reaction rate for the six reactions
was 3.2 mmol I.sup.-1 s.sup.-1 with a standard deviation of 0.5 mmol
I.sup.-1 s.sup.-1. For each reaction, the measured dioxygen consumption
was close to theory for complete oxidation of the vanadium content of the
solution, 100% as vanadium(IV), and the reactions proceeded at near
constant rate (the rate did not decelerate in proportion to the decreasing
vanadium(IV) concentration) up to >80% conversion of the vanadium(IV) to
vanadium(V).
Example 62
Oxidation of Reduced 0.30M {Li.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 }
with Dioxygen
A catalyst solution was prepared containing 0.15 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Li.sub.2 H.sub.3 PMo.sub.10 V.sub.2
O.sub.40 } (Example 21) and having -log[H.sup.+ ]=0.10 (0.8 mole per liter
hydrogen ion concentration). Two separate 100 milliliter solution samples
were each reduced and reacted with dioxygen two times in Reactor #2 under
the same nominal reaction conditions as in Example 61. The tests on the
separate solution samples were interspersed with the those of Example 61
and other experiments, with intervening reactor disassembly and
reassembly. The average initial dioxygen reaction rate for the four
reactions was 2.5 mmol I.sup.-1 s.sup.-1 with a standard deviation of 0.5
mmol I.sup.-1 s.sup.-1. For each reaction, the measured dioxygen
consumption was close to theory for complete oxidation of the vanadium
content of the solution, 100% as vanadium(IV), and the reactions proceeded
at near constant rate (the rate did not decelerate in proportion to the
decreasing vanadium(IV) concentration) up to >80% conversion of the
vanadium(IV) to vanadium(V).
Comparison with Example 61 shows that the measured rate of dioxygen
reaction for reduced 0.30M {Li.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 }
is not significantly different from that of reduced 0.30M {Li.sub.4
HPMo.sub.10 V.sub.2 O.sub.40 } under these conditions. The gas-liquid
mixing efficiency for these exemplified reaction is not sufficient to
reveal any differences in the chemical kinetic reactivity of the two
solutions with dioxygen which might be attributed to their different
hydrogen ion concentrations. This Example also demonstrates that the
present invention provides dioxygen reaction rates in
vanadium(IV)-polyoxoanion solutions having hydrogen ion concentrations at
least as great as 0.8 mole per liter when essentially all the vanadium(IV)
is oxidized to vanadium(V) which are multiplicatively superior to the
rates disclosed in the background references for solutions said to have
"pH" 1 and greater when oxidized.
Only with solutions having still greater hydrogen ion concentration than
that in the present Example were diminished chemical kinetic reactivities
with dioxygen revealed under the reaction conditions of the present
Example. For example, under these conditions, fully reduced 0.317M
{H.sub.4.9 PMo.sub.10.1 V.sub.1.9 O.sub.40 } (Example 10), having
-log[H.sup.+ ]=-0.07 when oxidized, initially reacts with dioxygen at the
essentially constant mass-transfer limited rate to about 40-60% conversion
of the vanadium(IV) to vanadium(V), after which chemical kinetics limited
rates were revealed, with the rate decelerating with greater than
first-order dependence on the remaining vanadium(IV) concentration. (The
fraction of vanadium(IV) converted at the mass-transfer limited rate will
decrease with increased mass-transfer rate provided by more efficient
gas-liquid mixing.) Even this solution, having -log[H.sup.+ ]<0 when
oxidized, can provide reaction rates with dioxygen for conversion of a
substantial fraction of the vanadium(IV) to vanadium(V) which exceed the
rates disclosed in the background references for solutions said to have
"pH" 1 and greater.
Example 63
Oxidation of Reduced Palladium-Free 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2
O.sub.40 } with Dioxygen
100 milliliter of 0.30M {Li.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 } (Example
22) was charged to Reactor #2 equipped with a single vertical baffle and
the gas phase in the autoclave was changed to 1 atmosphere dinitrogen.
0.81 milliliters hydrazine hydrate (14.25 millimoles hydrazine) was
injected into the solution and the solution was heated to 120.degree. C.
with gentle stirring. Dinitrogen evolution from hydrazine oxidation was
monitored by pressure increase, up to constant pressure. With very gentle
stirring of the solution, dioxygen was regulated into the autoclave to add
29 psi to the total autoclave pressure. The dioxygen reaction was then
initiated using an impeller stirring rate of 2000 RPM as previously
described. 12.9 millimole of dioxygen was consumed, corresponding to 91%
of the hydrazine reducing equivalents added to the solution. The initial
dioxygen reaction rate was 2.7 mmol I.sup.-1 s.sup.-1 and the reaction
proceeded at near constant rate (the rate did not decelerate in proportion
to the decreasing vanadium(IV) concentration) up to .about.90% of the
total oxygen consumption.
This reaction rate is not significantly different from that of Example 61,
in which a palladium salt was added in the 0.30M {Li.sub.4 HPMo.sub.10
V.sub.2 O.sub.40 } solution to catalyze the reduction of vanadium by
carbon monoxide. This demonstrates that palladium is not required in the
process of the present invention for the oxidation of vanadium(IV) to
vanadium(V).
Example 64
Oxidation of Reduced 0.30M {Li.sub.4.7 H.sub.2.3 PMo.sub.8 V.sub.4 O.sub.40
} with Dioxygen
100 milliliters of a catalyst solution containing 0.10 mM Pd(CH.sub.3
CO.sub.2).sub.2 dissolved in 0.30M {Li.sub.4.7 H.sub.2.3 PMo.sub.8 V.sub.4
O.sub.40 } (Example 31), having -log[H.sup.+ ]=1.48, was charged to
Reactor #2 equipped with a cage of four vertical baffles, fully reduced
with carbon monoxide, and reacted at 120.degree. C. with dioxygen at 30
psi partial pressure using an impeller stirring rate of 2000 RPM. Dioxygen
consumption ceased at 27.8 millimoles, corresponding to 93% of the
vanadium(IV) capacity of the solution, assuming 100% of vanadium was
initially reduced to vanadium(IV). The dioxygen reaction rate was
initially 5.4 mmol I.sup.-1 s.sup.-1 and the reaction proceeded at near
constant rate (the rate did not decelerate in proportion to the decreasing
vanadium(IV) concentration) up to .about.80% of the total oxygen
consumption.
Example 65
Oxidation of Reduced 0.30M {Li.sub.2.5 H.sub.4.5 PMo.sub.8 V.sub.4 O.sub.40
} with Dioxygen
Following the reaction of Example 64, Reactor #2 was drained, rinsed with
water, tided by heating, and charged with 100 milliliters of a catalyst
solution containing 0.10 mM Pd(CH.sub.3 CO.sub.2).sub.2 dissolved in 0.30M
{Li.sub.2.5 H.sub.4.5 PMo.sub.8 V.sub.4 O.sub.40 } (Example 29), having
-log[H.sup.+ ]=0.36, all without any disassembly of the reactor. The
solution was fully reduced with carbon monoxide and reacted with dioxygen
under the same conditions used in Example 64. Dioxygen consumption ceased
at 29.1 millimoles, corresponding to 97% of the vanadium(IV) capacity of
the solution, assuming 100% of vanadium was initially reduced to
vanadium(IV). The dioxygen reaction rate was initially 6.4 mmol I.sup.-1
s.sup.-1 and the reaction proceeded at near constant rate (the rate did
not decelerate in proportion to the decreasing vanadium(IV) concentration)
up to .about.80% of the total oxygen consumption.
Comparison with Example 64 shows that a diffusion limited dioxygen reaction
rate of a reduced 0.30M {Li.sub.p H.sub.(7-p) PMo.sub.8 V.sub.4 O.sub.40 }
solution having a hydrogen ion concentration substantially greater than
0.10 mole per liter when oxidized is not diminished relative to that of
one having a hydrogen ion concentration substantially less than 0.10 mole
per liter when oxidized.
Example 66
Oxidation of Reduced 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 }
with Dioxygen
100 milliliters of a catalyst solution containing 0.10 mM Na.sub.2
PdCl.sub.4 and 25.0 mM NaCl dissolved in 0.30M {Na.sub.3 H.sub.3 PMo.sub.9
V.sub.3 O.sub.40 } (Example 24), having -log[H.sup.+ ]=0.45, was charged
to Reactor #3 equipped with a cage of four vertical baffles and
alternately fully reduced with carbon monoxide and reacted at 110.degree.
C. with dioxygen at 36 psi partial pressure at an impeller stirring rate
of 2000 RPM until the dioxygen consumption ceased. Two cycles of reduction
and dioxygen reaction gave the reaction rates and dioxygen consumptions
listed in Table 9.
Example 67
Oxidation of Reduced 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 }
Containing Added Sodium Sulfate Salts with Dioxygen
Following the reaction of Example 66, Reactor #3 was drained, rinsed with
water, dried by heating, and charged with 100 milliliters of a catalyst
solution containing 0.10 mM Na.sub.2 PdCl.sub.4 and 25.0 mM NaCl dissolved
in the solution designated 0.30M {Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3
O.sub.40 }+1.5M Na.sub.1.7 H.sub.0.3 SO.sub.4 prepared as in Example 54
and having -log[H.sup.+ ]=0.45, all without any disassembly of the
reactor. (Except for the addition of the dissolved sulfate salts, this
solution has the same composition as the solution used in Example 66.) The
solution was alternately fully reduced with carbon monoxide and reacted
with dioxygen under the same conditions used in Example 66. Two cycles of
reduction and dioxygen reaction gave the reaction rates and dioxygen
consumptions listed in Table 9.
Comparison with Example 66 shows that the presence of the sulfate ions in
the present Example results in a reaction rate less than 50% of that
obtained in their absence.
TABLE 9
______________________________________
[sulfate] rate O.sub.2 reacted
Example mole/liter
mmol l.sup.-1 s.sup.-1
mmoles % theory
______________________________________
66 zero 3.3 26.2 117
3.2 28.3 126
67 1.5 1.5 23.4 104
1.6 22.6 100
______________________________________
Gas-liquid diffusion limited reaction rates are positively dependent on the
solubility of the gas in the liquid. The decrease in diffusion limited
rates of dioxygen reaction caused by the addition of sulfate salts is
reasonably attributable to a decrease in the solubility of dioxygen in the
aqueous solution. Chemical kinetic rates for reaction of dissolved oxygen
depend on the concentration of dissolved oxygen, and so also depend on
dioxygen solubility. Accordingly, a capability for increased dioxygen
reaction rates, whether diffusion limited or chemical kinetics limited,
may be provided in any vanadium(IV)-polyoxoanion solution which is
essentially free of sulfuric acid and sulfate ions.
With the benefit of the present invention, the teaching of the Matveev
patents and other background references that rates of dioxygen reaction
are appreciably diminished at decreasing "pH" values may now be understood
to reflect the increasing amounts of sulfuric acid added to decrease "pH".
That is, their diminished rate results not simply from the decreased "pH",
but in part or in whole from the increased sulfate concentration.
The present inventions have been shown by both description and
exemplification. The exemplification is only exemplification and cannot be
construed to limit the scope of the invention. Persons of ordinary skill
in the art will envision equivalents to the inventive solutions and
processes described by the following claims which are within the scope and
spirit of the claimed invention.
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